In 1970, when I was serving as a lieutenant in the US Navy and assigned to Admiral Thomas H Moorer, the chief of naval operations, I sometimes acted as a courier, taking documents to the White House. One evening I was dispatched with a package to the lower level of the West Wing of the White House, where there was a little waiting area near the Situation Room. It could be a long wait for the right person to come out and sign for the material, and after I had been waiting for a while a tall man with perfectly combed grey hair came in and sat down near me. His suit was dark, his shirt white and his necktie subdued. He was probably 25 to 30 years older than me and was carrying what looked like a file case or briefcase. He was very distinguished looking and had a studied air of confidence, the posture and calm of someone used to giving orders and having them obeyed instantly.

I could tell he was watching the situation very carefully. There was nothing overbearing in his attentiveness, but his eyes were darting about in a kind of gentlemanly surveillance. After several minutes, I introduced myself. "Lieutenant Bob Woodward," I said, carefully appending a deferential "sir".

"Mark Felt," he said.

I began telling him about myself, that this was my last year in the navy and I was bringing documents from Admiral Moorer's office. Felt was in no hurry to explain anything about himself or why he was there.

This was a time in my life of considerable anxiety about my future. I had graduated in 1965 from Yale, where I had a naval scholarship that required that I go into the navy after getting my degree. After four years of service, I had been involuntarily extended an additional year because of the Vietnam war.

During that year in Washington, I expended a great deal of energy trying to find things or people who were interesting. I had a college classmate who was going to clerk for Chief Justice Warren E Burger, and I made an effort to develop a friendship with that classmate. To quell my angst and sense of drift, I was taking graduate courses at George Washington University.

When I mentioned the graduate work to Felt, he perked up immediately, saying he had gone to night law school at GW in the 1930s before joining - and this is the first time he mentioned it - the FBI. While in law school, he said, he had worked full time for his home-state senator from Idaho. I said that I had been doing some volunteer work at the office of my congressman, John Erlenborn, a Republican from the district in Wheaton, Illinois, where I had been raised.

Felt and I were like two passengers sitting next to each other on a long airline flight with nowhere to go and nothing really to do but resign ourselves to the dead time. He showed no interest in striking up a long conversation, but I was intent on it. I finally extracted from him the information that he was an assistant director of the FBI in charge of the inspection division, an important post under director J Edgar Hoover. That meant he led teams of agents who went around to FBI field offices to make sure they were adhering to procedures and carrying out Hoover's orders. I later learned that this was called the "goon squad".

I peppered Felt with questions about his job and his world. As I think back on this accidental but crucial encounter - one of the most important in my life - I see that my patter probably verged on the adolescent. Since he wasn't saying much about himself, I turned it into a career-counselling session. I was deferential, but I must have seemed very needy. He was friendly, and his interest in me seemed paternal. Still, the most vivid impression I have is that of his distant but formal manner. I asked Felt for his phone number, and he gave me the direct line to his office.

When I warned Mardian that my days with the FBI were numbered, he assured me that Hoover wouldn't force me out. "He wouldn't dare," Mardian said. I disagreed, and when I told him I suspected that Hoover would misuse the logs when I was gone, he grew concerned. "I don't have the authority to make this kind of decision," he told me, "but I'll talk to people who do." A few days later, Mardian told me that "on presidential request" and "on the authority of the attorney general" he would personally take possession of the logs and correspondence. In May 1973, I learned that after our first meeting Mardian had flown to San Clemente to discuss the future whereabouts of the logs with President Nixon. Mardian kept something else from me too: he never mentioned that the logs would not be kept in his office, as I assumed, but in the White House. In all fairness to Mardian, whose intelligence and ability I still respect, I don't think that the logs were moved to the White House to obstruct justice, but to maintain security. When I turned in my inventory before leaving the FBI for the last time, I listed the logs and told Mark Felt that I had left them in Mardian's possession.

I was supposed to be jealous of Gray for having received the appointment as Acting Director instead of myself. They felt that my high position in the FBI gave me access to all the Watergate information and that I was releasing it to Woodward and Bernstein in an effort to discredit Gray so that he would be removed and I would have another chance at the job. Then there were those frequent instances when I had been much less than cooperative in responding to requests from the White House which I felt were improper. I suppose the White House staff had me tagged as an insubordinate. It is true I would like to have been appointed FBI director... but I never leaked information to Woodward and Bernstein or anyone else!

Much of the information that Deep Throat knew was known by many people. While it is impossible to know who might have whispered secrets to whom, thus broadening the circle of knowledge, working logically two particular bits of information that were given to Woodward by his friend easily point to Al Haig.

On March 5, 1973, Time magazine broke a story that the White House had wiretapped newsmen and White House aides in an effort to track down leaks. The White House denied the story was true, although it was true. Time had cracked this case, but they could not learn from their sources in the FBI and Justice Department who had been bugged. The records of the taps had been removed by Bill Sullivan, and passed by Bob Mardian to the White House. When the Time story broke, the records were in John Ehrlichman's safe.

When Woodward met with his friend in late February, shortly before Pat Gray's confirmation hearings, Deep Throat was able to tell Bob that Gray had been aware of these wiretaps and that the work was done by an "out-of-channels vigilante squad." This last piece of information could have been a deliberate effort to mislead Woodward, since it was not true. Deep Throat also gave Woodward the names of two people who had been tapped: "Hedrick Smith and Neil Sheehan of The New York Times." It is the revelation of these names that is the extraordinary information.

I found it interesting that, first, Deep Throat could state flatly that Gray knew about the taps, when he was also saying this was not an FBI operation, and when the Watergate special prosecutor would be unable to prove that Gray knew after an intense investigation with the full resources of the FBI, Justice Department, and several years of digging. Second, the only people who knew the names of those who had been tapped at the time the information was given to Woodward were Richard Nixon, Henry Kissinger, John Ehrlichman, John Mitchell, Bob Mardian, a very small group in the FBI, Bill Sullivan, Mark Felt, and the man who gave the FBI the names - Al Haig.

When you add to this the scarcely known secret that was given to Woodward about the "deliberate erasures" on the court-subpoenaed tape, Haig passes another test that uniquely qualifies him as the most likely person to have been Woodward's friend.

John Simkin's analysis is as good as any I've seen. The problem, however, isn't so much a question of ascertaining the identity of "Deep Throat," as it is of identifying Woodward's most important source. That Deep Throat was a composite and, as Adrian Havill has suggested, a "literary device," we may take for granted. (As I recall, Throat figured only incidentally in the first draft of All the President's Men. This changed when Woodward's editor, Alice Mayhew, realized the book needed a bit more excitement, and so urged Woodward to play up the role of man he met in the garage, the one with the sexy name. And so he did.

In the end, however, "Deep Throat" is whoever Woodward says he is, so long as it's someone with whom Woodward actually spoke. And if Woodward says Felt is Throat, then I guess Felt will have to carry that tag into the grave. But the really important questions - who was Woodward's most important source and why has he kept that person's identity secret for so long - are swept under the rug by Woodward's designation of Felt as Throat. Indeed, I think it's fair to say that Woodward is using Mark Felt ( the Deep Throat persona) in the same way that a magician uses misdirection to conceal what's actually going on.

The truth is, Woodward had many sources. Felt was one. Bobby Inman was another. And so on and on. His most important source, however, was undoubtedly the man identified in a CIA document entitled "Memorandum for the Record by Martin Lukoskie." At the time it was written, Mr. Lukoskie was an employee of the CIA's Central Cover Staff. The subject-line of his memo reads: "Meeting with Robert Foster Bennett and his Comments Concerning E. Howard Hunt, Douglas Caddy and the Watergate Five Incident." Lukoskie notes that the meeting with Bennett took place on July 10, 1972 in the Hot Shop (sic) Cafeteria in Washington.

Lukoskie was the CIA's liaison to the Robert R. Mullen Company, which had for years provided commercial cover for CIA officers around the world. (The firm's most important client was the Howard Hughes organization - which DNC Chairman Larry O'Brien had represented prior to Robert Maheu's ouster.)

Bennett was the Mullen Company's president, and Howard Hunt was one of its key employees. Lukoskie, then, was Bennett's case officer. And in his memo, the CIA officer reports Bennett's assertion that "when E. Howard Hunt was connected with the (Watergate) incident, reporters from the Washington Post and he (Bennett) thought the Washington Star tried to establish a "Seven Days in May" scenario with the Agency attempting to establish control over both the Republican and Democratic Parties so as to be able to take over the country. Mr. Bennett said he was able to convince them that course (sic) was nonsense." That the reporters were Woodward and Bernstein seems likely, since Lukoskie goes on to report that "Mr. Bennett...has now established a back door entry to the Edward Bennett Williams law firm which is representing the Democratic Party in its suit for damages resulting from the Watergate incident;. Mr. Bennett is prepared to go this route to kill off any revelation by Ed Williams of Agency association with the Mullen firm if such a development seems likely." (The Lukoskie memo is reprinted in the Appendix to Secret Agenda.)

Nine months after this memo was written, Lukoskie's boss at the CIA, Eric Eisenstadt, wrote a memo of his own. Entitled "Memorandum for the Deputy Director for Plans," the memo reported that "Bennett said...that he has been feeding stories to Bob Woodward of the Washington Post with the understanding that there be no attribution... Woodward is suitably grateful for the fine stories and by-lines which he gets and protects Bennett (and the Mullen Company)." In the same memo, Eisenstadt reports that Bennett spent hours persuading a Newsweek reporter that the Mullen Company "was not involved with the Watergate Affair." The memo goes on to report that Bennett helped to convince reporters for the Washington Star, the Washington Post and the Los Angeles Times that the CIA had not "instigated the Watergate affair." If I may quote myself and Secret Agenda: "As an example of Bennett's 'achievements,' Eisenstadt cited Bennett's inspiration of a Newsweek article entitled 'Whispers about Colson' and a Washington Post story about Hunt's investigation of Senator Edward Kennedy."

Clearly, Robert Bennett was a key source - and, quite possibly, Woodward's most important source. Whether he was Deep Throat or not is, in the end, for Woodward to say. But it seems to me that if Woodward's most important source was, in fact, shilling for the CIA - was, in fact, a CIA agent hell-bent on manipulating the Watergate story - then the Washington Post reporter had good reason to keep the identity of that source secret for as long as he could.. Because, of course, if this was indeed the case, then Woodward was less a hero of investigative journalism than a stooge for Langley. And if I am right about that, then pinning the Deep Throat label on the addled Mark Felt was no more than a cynical attempt to end the on-going speculation about Deep Throat's identity - which threatened to bring Woodward's reputation crashing down around him.

Breaking a silence of 30 years, former FBI official W. Mark Felt stepped forward Tuesday as "Deep Throat," the secret Washington Post source who helped bring down President Richard M. Nixon during the Watergate scandal. Within hours, the newspaper confirmed his assertion.

"It's the last secret" of the story, said Benjamin C. Bradlee, the newspaper's top editor at the time the riveting political drama played out three decades ago.

The revelation tumbled out in stages during the day - first when a lawyer quoted Felt in a magazine article as having said he was the source; then when the former FBI man's family issued a statement hailing him as a "great American hero." Within hours, the newspaper confirmed Felt's assertion, ending one of the most enduring mysteries in American politics and journalism.

"I'm the guy they used to call "Deep Throat,' " Felt, the former No. 2 official at the FBI, was quoted as saying in Vanity Fair.

He kept his secret even from his family for almost three decades before his declaration.

Felt, now 91, lives in Santa Rosa, Calif., and is said to be in poor mental and physical health because of a stroke. His family did not immediately make him available for comment, asking the media to respect his privacy "in view of his age and health."

A grandson, Nick Jones, read a statement. "The family believes that my grandfather, Mark Felt Sr., is a great American hero who went well above and beyond the call of duty at much risk to himself to save his country from a horrible injustice," it said.

In a statement issued later, Watergate reporters Bob Woodward and Carl Bernstein said, "W. Mark Felt was "Deep Throat' and helped us immeasurably in our Watergate coverage. However, as the record shows, many other sources and officials assisted us and other reporters for the hundreds of stories that were written in the Washington Post about Watergate."

Among other things, "Deep Throat" urged the reporters to follow the money trail - from the financing of burglars who broke into Democratic National Committee offices to the financing of Nixon's re-election campaign. The reporters and Bradlee had kept the identity of "Deep Throat" secret at his request, saying his name would be revealed upon his death. But then Felt revealed it himself.

Even the existence of "Deep Throat," nicknamed for an X-rated movie of the early 1970s, was kept secret for a time. Woodward and Bernstein revealed their reporting had been aided by a Nixon administration source in their best-selling book "All the President's Men."

A hit movie starring Robert Redford as Woodward, Dustin Hoffman as Bernstein and Hal Holbrook as "Deep Throat" was made in 1976. In the film, Holbrook's shadowy, cigarette-smoking character met Redford in dark parking garages and provided clues about the scandal.

The source's identity had sparked endless speculation. Nixon chief of staff Alexander M. Haig Jr., acting FBI Director L. Patrick Gray III, White House Counsel John W. Dean III and his deputy, Fred Fielding, and former Nixon deputy counsel John Sears were among those mentioned.

Felt himself was mentioned several times over the years as a candidate for "Deep Throat," but he regularly denied that he was.

"I would have done better," Felt told the Hartford Courant in 1999. "I would have been more effective. "Deep Throat' didn't exactly bring the White House crashing down, did he?"

Felt had hopes that he would be the next FBI director, but Nixon instead appointed Gray, an administration insider who was an assistant attorney general.

The Vanity Fair article, by California lawyer John D. O'Connor, described Felt as conflicted over his role in the Watergate revelations and over whether he should publicly reveal who he was.

A Nixon associate who wound up behind bars, G. Gordon Liddy, said he did not consider Felt a hero for going to the Post reporters.

"If he were interested in performing his duty, he would have gone to the grand jury with his information," Liddy, who was finance counsel at Nixon's reelection committee and helped direct the break-in, said on CNN.

According to the article, Felt once told his son, Mark Jr., that he did not believe being the Post's key confidential source on Watergate "was anything to be proud of.... You (should) not leak information to anyone."

Felt was convicted in the 1970s for authorizing illegal break-ins at homes of people associated with the radical Weather Underground. He was pardoned by President Ronald Reagan in 1981.

Somewhat to my astonishment, Felt was an admirer of Hoover. He appreciated his orderliness and the way he ran the bureau with rigid procedures and an iron fist. Felt said he appreciated that Hoover arrived at the office at 6.30 each morning and everyone knew what was expected. The Nixon White House was another matter, Felt said. The political pressures were immense without being specific. I believe he called it "corrupt" and sinister. Hoover, Felt and the old guard were the wall that protected the FBI, he said.

At the time, pre-Watergate, there was little or no public knowledge of the acrimony between the Nixon White House and Hoover's FBI. The Watergate investigations later revealed that in 1970, a young White House aide, Tom Charles Huston, had come up with a plan to authorise the CIA, the FBI and military intelligence units to intensify electronic surveillance of "domestic security threats", authorise illegal opening of mail and lift the restrictions on surreptitious entries or break-ins to gather intelligence.

Huston warned in a top-secret memo that the plan was "clearly illegal". Nixon initially approved the plan anyway. Hoover strenuously objected, because eavesdropping, opening mail and breaking into the homes and offices of domestic security threats were basically the FBI bailiwick and the bureau didn't want competition. Four days later, Nixon rescinded the Huston plan.

During this period, Felt had to stop efforts by others in the bureau to "identify every member of every hippie commune" in the Los Angeles area, or to open a file on every member of Students for a Democratic Society. None of this surfaced directly in our discussions, but clearly he was a man under pressure, and the threat to the integrity and independence of the bureau was real and seemed uppermost in his mind.

On July 1 1971 - about a year before Hoover's death and the Watergate break-in - Hoover promoted Felt to number-three official in the FBI. Though Hoover's sidekick, Clyde Tolson, was technically the number-two official, Tolson was ill and did not come to work many days, meaning he had no operational control of the bureau. Thus, my friend became the day-to-day manager of all FBI matters, as long as he kept Hoover and Tolson informed, or sought Hoover's approval on policy matters.

In August, a year after my failed tryout, Rosenfeld hired me. I started at the Post the next month.

Though I was busy in my new job, I kept Felt on my call list and checked in with him. He was relatively free with me but insisted that he, the FBI and the justice department be kept out of anything I might use indirectly or pass on to others. He was stern and strict about those rules with a booming, insistent voice. I promised, and he said that it was essential that I be careful. The only way to ensure that was to tell no one that we knew each other or talked or that I knew someone in the FBI or justice department. No one.

About 9.45am on May 2 1972, Felt was in his office at the FBI when an assistant director came to report that Hoover had died. Felt was stunned. For practical purposes, he was next in line to take over the bureau. Yet Felt was soon to be visited with immense disappointment. Nixon nominated L Patrick Gray III to be acting director. Gray was a Nixon loyalist going back years. He had resigned from the navy in 1960 to work for candidate Nixon during the presidential contest that Nixon lost to John F Kennedy.

As best I could tell, Felt was crushed, but he put on a good face. "Had I been wiser, I would have retired," Felt wrote.

On May 15, less than two weeks after Hoover's death, a lone gunman shot Alabama Governor George C Wallace, then campaigning for president, at a shopping centre. The wounds were serious, but Wallace survived. Wallace had a strong following in the deep South, an increasing source of Nixon's support. Wallace's spoiler candidacy four years earlier in 1968 could have cost Nixon the election that year, and Nixon monitored Wallace's every move closely as the 1972 presidential contest continued.

That evening, Nixon called Felt - not Gray, who was out of town - at home for an update. It was the first time Felt had spoken directly with Nixon. Felt reported that Arthur H Bremer, the would-be assassin, was in custody but in the hospital because he had been roughed up and given a few bruises by those who subdued and captured him after he shot Wallace.

"Well, it's too bad they didn't really rough up the son of a bitch!" Nixon told Felt.

Felt was offended that the president would make such a remark. Nixon was so agitated, attaching such urgency to the shooting, that he said he wanted full updates every 30 minutes from Felt on any new information that was being discovered in the investigation of Bremer.

In the following days I called Felt several times and he very carefully gave me leads as we tried to find out more about Bremer. It turned out that he had stalked some of the other candidates, and I went to New York to pick up the trail. This led to several front-page stories about Bremer's travels, completing a portrait of a madman not singling out Wallace but rather looking for any presidential candidate to shoot. On May 18, I did a page-one article that said, "High federal officials who have reviewed investigative reports on the Wallace shooting said yesterday that there is no evidence whatsoever to indicate that Bremer was a hired killer."

It was rather brazen of me. Though I was technically protecting my source and talked to others besides Felt, I did not do a good job of concealing where the information was coming from. Felt chastised me mildly. But the story that Bremer acted alone was a story that both the White House and the FBI wanted out.

A month later, on Saturday June 17, the FBI night supervisor called Felt at home. Five men in business suits, pockets stuffed with $100 bills, and carrying eavesdropping and photographic equipment, had been arrested inside the Democrats' national headquarters at the Watergate office building at about 2.30am.

By 8.30am, Felt was in his office at the FBI, seeking more details. About the same time, the Post's city editor woke me at home and asked me to come in to cover an unusual burglary.

The first paragraph of the front-page story that ran the next day in the Post read: "Five men, one of whom said he is a former employee of the Central Intelligence Agency, were arrested at 2.30am yesterday in what authorities described as an elaborate plot to bug the offices of the Democratic National Committee here." The next day, Carl Bernstein and I wrote our first article together, identifying one of the burglars, James W McCord Jr, as the salaried security coordinator for Nixon's reelection committee. On Monday, I went to work on E Howard Hunt, whose phone number had been found in the address books of two of the burglars with the small notations "W House" and "WH" by his name.

This was the moment when a source or friend in the investigative agencies of government is invaluable. I called Felt at the FBI, reaching him through his secretary. It would be our first talk about Watergate. He reminded me how he disliked phone calls at the office but said the Watergate burglary case was going to "heat up" for reasons he could not explain. He then hung up abruptly.

I was tentatively assigned to write the next day's Watergate bugging story, but I was not sure I had anything. Carl had the day off. I picked up the phone and dialled 456-1414 - the White House - and asked for Howard Hunt. There was no answer, but the operator helpfully said he might be in the office of Charles W Colson, Nixon's special counsel. Colson's secretary said Hunt was not there but might be at a PR firm where he worked as a writer. I called and reached Hunt and asked why his name was in the address book of two of the Watergate burglars.

"Good God!" Hunt shouted before slamming down the phone. I called the president of the PR firm, Robert F Bennett, who is now a Republican US senator from Utah. "I guess it's no secret that Howard was with the CIA," Bennett said blandly.

It had been a secret to me, and a CIA spokesman confirmed that Hunt had been with the agency from 1949 to 1970. I called Felt again at the FBI. Colson, White House, CIA, I said. What did I have? Anyone could have someone's name in an address book. Felt sounded nervous. He said - off the record, meaning I could not use the information - that Hunt was a prime suspect in the burglary at the Watergate for many reasons beyond the address books. So reporting the connections forcefully would not be unfair.

In July, Carl went to Miami, home of four of the burglars, on the money trail, and he ingeniously tracked down a local prosecutor and his chief investigator, who had copies of $89,000 in Mexican cheques and a $25,000 cheque that had gone into the account of Bernard L Barker, one of the burglars. We were able to establish that the $25,000 cheque had been campaign money that had been given to Maurice H Stans, Nixon's chief fundraiser, on a Florida golf course. The August 1 story on this was the first to tie Nixon campaign money directly to Watergate.

I tried to call Felt, but he wouldn't take the call. I tried his home and had no better luck. So one night I showed up at his Fairfax home. It was a plain-vanilla, perfectly kept suburban house. His manner made me nervous. He said no more phone calls, no more visits to his home, nothing in the open. I did not know then that in Felt's earliest days in the FBI, during the second world war, he was assigned to work on the general desk of the espionage section. Felt learned a great deal about German spying in the job, and after the war spent time keeping suspected Soviet agents under surveillance. So at his home in Virginia that summer, Felt said that if we were to talk it would have to be face to face, where no one could observe us.

I said anything would be fine with me.

We would need a preplanned notification system - a change in the environment that no one else would notice or attach any meaning to. I didn't know what he was talking about.

If you keep the drapes in your apartment closed, open them and that could signal me, he said. I could check each day or have them checked, and if they were open we could meet that night at a designated place. I liked to let the light in at times, I explained.

We needed another signal, he said, indicating that he could check my apartment regularly. He never explained how he could do this. Feeling under some pressure, I said that I had a red cloth flag - the kind used as a warning on long truck loads - that a girlfriend had found on the street. She had stuck it in an empty flowerpot on my apartment balcony. Felt and I agreed that I would move the flowerpot with the flag, which usually was in the front near the railing, to the rear of the balcony if I urgently needed a meeting. This would have to be important and rare, he said sternly. The signal, he said, would mean we would meet that same night at about 2am on the bottom level of an underground garage just over the Key Bridge in Rosslyn.

Felt said I would have to follow strict countersurveillance techniques. How did I get out of my apartment?

I walked out, down the hall, and took the elevator.

Which takes you to the lobby? he asked.

Yes.

Did I have back stairs to my apartment house?

Yes.

Use them when you are heading for a meeting. Do they open into an alley?

Yes.

Take the alley. Don't use your own car. Take a taxi to several blocks from a hotel where there are cabs after midnight, get dropped off and then walk to get a second cab to Rosslyn. Don't get dropped off directly at the parking garage. Walk the last several blocks. If you are being followed, don't go down to the garage. I'll understand if you don't show. The key was taking the necessary time - one to two hours to get there. Be patient, serene. Trust the pre-arrangements. There was no fallback meeting place or time. If we both didn't show, there would be no meeting.

Felt said that if he had something for me, he could get me a message. He quizzed me about my daily routine, what came to my apartment, the mailbox, etc. The Post was delivered outside my apartment door. I did have a subscription to the New York Times. A number of people in my apartment building near Dupont Circle got the Times. The copies were left in the lobby with the apartment number. Mine was 617, and it was written clearly on the outside of each paper. Felt said if there was something important he could get to my New York Times - how, I never knew. Page 20 would be circled, and the hands of a clock in the lower part of the page would be drawn to indicate the time of the meeting that night, probably 2am, in the same parking garage.

The relationship was a compact of trust; nothing about it was to be discussed or shared with anyone, he said.

How he could have made a daily observation of my balcony is still a mystery to me. At the time, before the era of intensive security, the back of the building was not enclosed, so anyone could have driven in to observe my balcony. In addition, my balcony and the back of the apartment complex faced on to a courtyard that was shared with other buildings. My balcony could have been seen from dozens of apartments or offices, as best I can tell.

Esquire had it wrong; Atlantic Monthly had it right.

Leonard Garment's book missed the mark; Ronald Kessler's was on the money.

William Gaines' college journalism class flunked the test; Chase Culeman-Beckman's high-school history paper, although he didn't get an "A" when he turned it in six years ago, should have put him at the head of the class.

A 30-year national guessing game is over: W. Mark Felt, former associate director of the FBI, has revealed to Vanity Fair magazine that he was Deep Throat, the anonymous source who leaked information to The Washington Post about President Nixon's Watergate cover-up.

The Post confirmed on its Web site yesterday that Felt indeed was Deep Throat.

Thus ends one of the nation's longest-running modern-day mysteries.

Felt, it turns out, is the final answer — and not too many had it right. One can rightfully expect in weeks ahead some apologies from those who guessed wrong, and a few "I-told-you-so's" from those who nailed it, including Culeman-Beckman.

Born well after Watergate, Culeman-Beckman was only 8 years old when, he says, Jacob Bernstein, a son of Watergate reporter Carl Bernstein, revealed Deep Throat's identity to him during playtime at summer day camp in 1988.

Except for telling his mom, Culeman-Beckman would keep the secret for nearly 10 years — until spilling the beans in a high-school research paper.

In a 1999 Hartford Courant article about Culeman-Beckman's disclosure (which was printed in The Seattle Times), Felt denied he was Deep Throat. Bernstein said neither he nor reporting partner Bob Woodward had ever told their wives, children or anyone else Deep Throat's identity.

In fact, the two men had agreed not to divulge his identity until after his death. They took pains to exclude any documents identifying him when they sold their Watergate papers two years ago to the University of Texas. And neither, initially, would confirm yesterday that Felt was Deep Throat. By late afternoon, though, Woodward, Bernstein and former Washington Post Executive Editor Ben Bradlee said in an article posted on the paper's Web site that Felt was the anonymous source.

Since Woodward and Bernstein's best-selling book, "All the President's Men," disclosed the existence of Deep Throat, speculation has been rampant, and entire books have been written about his identity.

Some, including the authors of "Silent Coup: The Removal of a President," suspected Alexander Haig, chief of staff under Nixon. Some suspected Nixon adviser David Gergen, whom Esquire magazine in 1976 picked as the No. 1 candidate for Deep Throat.

"Watergate: the Secret Story," a documentary by CBS News and The Washington Post, concluded it was acting FBI director L. Patrick Gray.

Leonard Garment, Nixon's special counsel and author of "In Search of Deep Throat: The Greatest Political Mystery of Our Time," opted for fellow presidential lawyer John Sears.

Fred Fielding, deputy White House counsel to John Dean, was the choice of both Watergate conspirator H.R. Haldeman in his book, "The Ends of Power," and William Gaines' journalism classes at the University of Illinois, which spent four years investigating Deep Throat's identity.

A relative handful of guessers had it right.

Felt was seen as the most likely suspect in "The Bureau: The Secret History of the FBI," a book by Kessler, a former Washington Post reporter; in "Deep Throat: An Institutional Analysis," a 1992 Atlantic Monthly article by James Mann, a former colleague of Woodward's at the Post; and in articles in Washingtonian magazine by its editor, Jack Limpert.

Felt was suspected by the White House, according to the Nixon tapes:

Nixon: "Well, if they've got a leak down at the FBI, why the hell can't Gray tell us what the hell is left? You know what I mean? ... "

Haldeman: "We know what's left, and we know who leaked it."

Nixon: "Somebody in the FBI?"

Haldeman: "Yes, sir. Mark Felt. ... If we move on him, he'll go out and unload everything. He knows everything that's to be known in the FBI. He has access to absolutely everything. ... "

Nixon: "What would you do with Felt? You know what I'd do with him, the bastard? Well that's all I want to hear about it."

Haldeman: "I think he wants to be in the top spot."

Nixon: "That's a hell of a way for him to get to the top."

Felt, in his own memoir, "The FBI Pyramid: Inside the FBI," denied being Deep Throat and said he met with Woodward only once.

The name meant nothing to Culeman-Beckman when he heard it in 1988. Now a graduate student at Cornell University, he could not be reached for comment yesterday.

"I'm 100 percent sure that Deep Throat was Mark Felt," he quoted Bernstein's son as saying. "He's someone in the FBI." He told The Hartford Courant that the boy attributed the information to his father.

After the article, Bernstein, Jacob and his mother, writer and movie director Nora Ephron, all denied that Bernstein had told anyone the identity of "Deep Throat."

To Culeman-Beckman, turnabout was fair play.

"They've been cute about it long enough," Culeman-Beckman said then. "I just think if it's fair of them to dethrone a president, for all intents and purposes, and not tell anyone their source, I don't see why it's not fair for a person like myself to come forward. ... Let the cards fall where they may. There's a chance this could be the answer to one of the greatest political mysteries of our time."

Curiously enough, it was.

History professor Joan Hoff of Montana State University, an expert on the Watergate scandal, finds it interesting that Bob Woodward is claiming that he had a close relationship with former FBI official Mark Felt, now identified as Deep Throat, when Felt suffers from serious health problems, including dementia, and can’t deny it. “It’s just like when he said he interviewed (former CIA director Bill) Casey when Casey was comatose,” she says.

Len Colodny, co-author of Silent Coup, about the “removal” of President Nixon, finds the identification of Mark Felt as Deep Throat to be rather remarkable: “A Deep Throat who can’t talk.”

The fact is, as AIM founder Reed Irvine documented, Woodward has been known to make things up. Woodward’s Casey “interview” is a case in point. As Reed noted, “In his 1987 book, Veil, Woodward claimed he had interviewed William J. Casey, the CIA director, after Casey had brain surgery and could not speak intelligibly. Woodward didn’t know that, and he made up an interview in which Casey is supposed to have spoken 19 intelligible words. It was clear that this was a falsification not only because of Casey’s condition, but because his hospital room was guarded and Woodward was never admitted to it.”

Hoff believes the identification of Deep Throat is part of “an orchestrated publicity stunt on the part of the Post and Woodward” because Woodward plans to publish his own book on Felt. “Lo and behold,” says Hoff, “Felt’s family decides he’s Deep Throat and Felt can’t say whether he is or not, and we get the big story.”

In fact, despite his serious health problems, Felt can still utter a few words. He was captured on film outside his home yesterday saying that he enjoyed the publicity and that, “I’ll arrange to write a book or something, and collect all the money I can.” A New York Times account indicates that members of the Felt family have been envious of the money that will be made from the Deep Throat disclosures and that they were trying to pursue their own book deal independent of Woodward after he rebuffed their pleas for a collaborative effort.

Felt seems to have been a source of some kind for Woodward. But was he the source known as Deep Throat? Hoff isn’t the only one who has some doubts.

Colodny says that what is known about Felt “doesn’t match what Woodward wrote in his book. He describes Deep Throat as someone he had known for a long time and had many discussions about power in Washington and so on. There’s not a shred of evidence that Felt is that person.”

In the June 2 Post, Woodward describes for the first time the details of his “friendship” with Felt. They are said to have met accidentally when Woodward, then a young Navy Lieutenant, was delivering Navy documents to the White House in 1970. Hoff points out that Felt, because of his severe memory problems, can’t deny any of this and the account “is based only and exclusively on Woodward’s word.”

But there are other reasons to doubt that Felt is Deep Throat.

Colodny and Hoff point to the claim in the Woodward/Bernstein book, All the President’s Men, that Deep Throat provided the Post reporters exclusive information about the “deliberate erasures,” as “Throat” told Woodward in November of 1973, on the White House tapes. “There’s no reason to believe that Felt had access to that information because it was closely held in the White House,” says Colodny, “and Felt had left the FBI in April - six months earlier.”

Hoff agrees. “It’s conceivable that as the second in command at the FBI, the deputy director, he could have gotten information from somebody about this,” she said. “But I don’t think he gave them this information. I think it was somebody in the White House. At that point, the White House was so embattled over the tapes and the possible subpoena (of them), there were only 3 or 4 people who had access to those tapes.”

That means, apparently, that either Felt is not Deep Throat or that he had his own Deep Throat.

But if Felt did somehow have access to that information and provided it to Woodward, important questions are raised.

“The guy is deputy director of the FBI,” Colodny says. “Why is he not protecting the tapes? Why is he not arresting the people who are doing this? Why doesn’t he go to (Watergate Judge John) Sirica’s court, which is hearing this? He’s a sworn law enforcement officer. He knows there’s a crime being committed. But instead of doing something about it, he goes in a garage and talks to Woodward.”

Hoff makes the same basic point. “He is the top law enforcement officer in the country because there’s only an acting director (of the FBI) at that point,” says Hoff. “Why didn’t he go to Sirica or a grand jury and blow the story open?”

If Felt was concerned about the hostility between the FBI and President Nixon, Hoff counters, “This is the very story that he could have killed the Nixon Administration with. Why in God’s name would a top law enforcement officer meet in a garage with a rookie reporter and give him this information? It makes no sense.”

Hoff predicts that the story will rebound to the discredit of Woodward. It’s another flashy story, she concedes, “but I think they made a mistake in choosing Felt.”

Last February 4, when the University of Texas in Austin opened the Bob Woodward and Carl Bernstein Watergate papers (for which it had paid them $5 million), Hoff participated in a symposium with Woodward and suggested that he put Deep Throat on videotape. Hoff wrote that she told Woodward that “he should video tape that individual as soon as possible so the public could be sure of the authenticity of the man Woodward would ultimately reveal as Deep Throat when the person could not deny it.”

Of course, this should have been done years ago. The Felt family has affirmed the Deep Throat designation but it’s now clear that they had a financial interest in doing so as well. And the questions about the conspiracy behind the Watergate conspiracy will be shunted aside and will remain unanswered.

It was one of America's greatest mysteries: Who was the anonymous source who had leaked information about the Watergate scandal that led to the resignation of US President Richard Nixon in 1974?

Mark Felt, a former deputy head of the FBI, has revealed that it was he who made the suggestion that led to the discovery of the link between the burglary at the Democratic National Committee HQ in Washington's Watergate complex in June 1972, and the financing of Nixon's reelection campaign.

For decades, the informant was known only as Deep Throat. He was the shadowy, chain-smoking character played by Hal Holbrook in the hit movie All the President's Men starring Robert Redford and Dustin Hoffman.

Mr Felt, who was responsible for investigating the burglary, has figured prominently in the 30-year guessing game about Deep Throat's identity.

But he repeatedly denied that he was the source who met Washington Post reporters Bob Woodward and Carl Bernstein in underground car parks to provide clues to the scandal.

Mr Felt, now 91, lives in retirement in Santa Rosa, California. According to reports, he has lived for decades in the belief that he betrayed his FBI badge by disclosing government secrets.

On Tuesday, his lawyer John O'Connor told US media: "Mark felt that he was somehow a dishonourable guy, an FBI agent who was disloyal, who leaked when he shouldn't have leaked. He kept saying an FBI agent doesn't do this."

Mr Felt's family only learned of his secret three years ago and, according to Mr O'Connor, they talked to him and helped convince him that he "was a hero".

"After talking to him for two to three years, probably for the last six to nine months, he was really convinced he was a hero. He knows he did the right thing. He knows he had to breach his code of ethics to save the country."

Mr Felt's son, Mark Junior, told Vanity Fair in an article detailing the revelation: "He would not have done it if he didn't feel it was the only way to get around the corruption in the White House and Justice Department. He was tortured inside, but never would show it."

The former FBI man unmasked as "Deep Throat' probably won't be prosecuted for sharing information with reporters during the Watergate scandal, Attorney General Alberto Gonzales indicated Friday.

"It happened a long time ago," Gonzales said of W. Mark Felt's conduct 30 years ago, when he was the No. 2 man at the FBI. "The department has a lot of other priorities."

Gonzales declined to characterize Felt as either hero or villain.

"I will leave it to history to make that determination," he said, echoing comments by President Bush.

Felt, now 91, provided critical tips about criminal wrongdoing at the White House to Washington Post reporter Bob Woodward during the Watergate scandal.

It is unclear whether he broke any laws, but some former members of the Nixon administration have said the information he revealed was confidential.

Last week, another one of those irresistible TV occasions came along when 91-year-old Mark Felt, who had been the No. 2 official at the FBI back in the early 1970s, acknowledged that he was the mysterious "Deep Throat" who systematically fed critical information to the Washington Post's Bob Woodward during that newspaper's lonely and courageous investigation of the events we now call Watergate. Felt was the greatest anonymous source we've ever seen.

Because it led to Richard Nixon's resignation as president, Watergate was the biggest political story of the 20th century in these United States. Given Deep Throat's critical role in helping a single newspaper unravel the sordid tale of corruption, intrigue and deceit that was leading inexorably to Nixon's impeachment, the tipster's identity was a compelling mystery.

As soon as the mystery was solved, the debate about the rectitude of the nation's most famous whistle-blower began. David Gergen, an aide to four presidents, stated his views on at least four different programs within hours of Felt's admission. Gergen, painfully reluctant to applaud Felt, was more moderate and responsible than most; others with similar ties to the Republican Party were downright snide about Felt and practically branded him a traitor.

The most offensive, I thought, was Chuck Colson, who found religion while serving a term in prison for misdeeds he committed while serving as the president's special counsel during the Watergate scandal. Now a man of God, he gave CNN's Aaron Brown no sign that the word "forgiveness" is part of his language. Mark Felt, he insisted, should have reported his misgivings to his superiors rather than spill the beans to the (ugh) press.

But look who Felt's superiors were: John Mitchell, the attorney general, and L. Patrick Gray III, the acting head of the FBI. We now know what Felt knew – that Mitchell was deeply involved in Watergate, at least the cover-up, which is what finally brought Nixon down. And Gray, a former assistant attorney general with no FBI experience, was loyal to the president who had appointed him to succeed the late J. Edgar Hoover, who was a greatly flawed character whom Nixon knew he could never control.

And of course we also know that Nixon himself was at the very center of the scandal. Colson apparently would have us believe Mitchell and Gray would have done something noble and good with Felt's reports. So, why can't we believe him?

The infamous Nixon tapes revealed that when the president was told that Felt might be the Post's source, he wondered aloud if Felt was a Catholic. No, he was told by his chief of staff, H.R. Haldeman, he's a Jew. And Nixon replied: "[Expletive], [the bureau] put a Jew in there?" And Haldeman responded "Well, that could explain it." Incidentally, Felt is not Jewish.

To many Americans, Felt was not the whistleblower who risked all to save US democracy but a self-serving rat who was just as big a danger to democracy as Nixon and his band of crooked advisers.

For these people, the Deep Throat epithet accurately conveys a sense of the political gutter they believe Felt occupies.

Not surprisingly, this debate has tended to be along party lines, with Democrats by and large embracing Felt as a courageous man of honour, the patron saint of whistleblowers.

Republicans, on the other hand, have targeted Felt's repeated breach of his oath of office, namely his release of confidential government information to Woodward and his failure to report his evidence of White House criminality to prosecutors.

Some, such as former Nixon speechwriter Pat Buchanan, have brutally dismissed Felt as a "traitor". Others, such as former Nixon chief counsel Charles Colson, have been more considered.

Colson said Felt's unique position in the intelligence community deprived him of the right to become a whistleblower.

"He had in his hands about the most sensitive portfolio in the US government and I think he abused it," Colson said this week.

"Do you want to live in a country where the deputy director of the FBI, who has access to the files of half the American people -- top-secret files -- feels free to give them out because he has a higher calling? To me, that's a pretty scary proposition."

Colson also pointed to the hypocrisy of Felt leaking when he was later convicted of organising the same kind of illegal Watergate-style burglaries against student radicals. In a strange twist, Nixon testified on Felt's behalf at his trial.

"I'm very sorry for Mark Felt," Colson said. "I liked him, I'm very sorry he leaves as Deep Throat. That's going to be on his tombstone and that is not a good legacy."

Former Nixon chief of staff Alexander Haig, one of those always high on the list of Deep Throat suspects, said a true man of honour caught in Felt's position would have resigned.

"If you see something that your conscience tells you you can't live with, then you resign and you take whatever action you can," Haig said this week.

"Sometimes you just resign. I've resigned from several presidencies for what I couldn't agree with. But you do resign. You don't have it both ways. You don't stay in a government position while you're leaking secrets to the outside newspapers."

In a taped phone conversation from May 12, 1973, Nixon told Haig that Felt was a "goddamn traitor" and told Haig to watch him carefully. Haig had told Nixon in 1973 that: "We've got to be careful as to when we cut his nuts off."

Gordon Liddy, the Nixon agent who was jailed for organising the 1972 break-in at the Democratic campaign headquarters in the Watergate building, said Felt's duty was to seek a grand jury indictment if he had evidence of White House criminality, a remark that earned a swift rebuke from Ben Bradlee, the Washington Post editor who backed Woodward and Bernstein.

"Liddy is a common crook," Bradlee said. "For these people to talk about the immorality of Deep Throat makes me laugh."

Of course the question of Felt's morality turns largely on his motivation for becoming Deep Throat in the first place. Was Felt, as a Post columnist Richard Cohen claimed this week, a man who "took seriously all that stuff about duty and loyalty and the American Way"?

Or was he just angry at being passed over by Nixon as head of the FBI after the death of J.Edgar Hoover and decided a revenge play in the media was the best way to get even?

Sadly, it seems the world will never hear from Felt on this critical point. At 91, and with a severe stroke behind him, he reportedly has no clear memory of the Watergate era, a factor likely to limit the cash value of his sudden celebrity.

Felt's last word on the subject came in 1999, on the 25th anniversary of Nixon's resignation, when he told a reporter that it would be "terrible" if someone in his position had been Deep Throat. "This would completely undermine the reputation that you might have as a loyal employee of the FBI," he said. "It just wouldn't fit at all."

This week, Felt, frail and almost clownish, was capable only of parroting the financial agenda of his family. "I'll arrange to write a book or something, and collect all the money I can," he told reporters outside his daughter's California home.

But that day publisher Judith Regan revealed that negotiations over a possible book deal had collapsed because of serious concerns that Felt was no longer of sound mind.

We were wrong. We had to accept we were wrong when on May 31, 2005, Bob Woodward, the famous Washington Post reporter, revealed that his super-secret source in the Watergate investigation of the Nixon Administration was Mark Felt, second in command at the FBI.

I had my class in investigative reporting at the University of Illinois at Urbana-Champaign make a systematic approach to finding the identity of that source who for more than 30 years was known only as Deep Throat.

My students over 12 semesters poured over FBI reports, congressional testimony, White House documents in the National Archives and autobiographies of Watergate figures. We started with the premise that everything Woodward wrote or spoke about Deep Throat was true to the best of his knowledge at the time. At the start, everyone was a suspect. Then we started narrowing the field.

We were aware of Mark Felt. There had been several claims that he was Deep Throat but we eliminated everyone in the FBI for several reasons.

It was known that Throat provided information from May 1972 until November 1973, according to Woodward and Carl Bernstein's book, All The President's Men. Felt had left the FBI in June 1973. At that time, the FBI was not directly involved in the Watergate investigation. It had been taken over by the staff of a special prosecutor.

In November 1973, according to the book, Throat told Woodward by phone that the Nixon tapes had gaps of a suspicious nature that could have been deliberate. When the students checked the newspaper reports of that week, they found that quotation from Throat to be attributed to a White House source. The FBI is an agency of the Justice Department, outside the gates of the White House.

A similar circumstance was found when students visited the Harry Ransom Research Center at the University of Texas that purchased Woodward and Bernstein's notes. Students located a report to Woodward from Throat that explained the transactions involved in checks from a Mexican bank that had gone into one of the Watergate burglar's bank account. When that was written about in the newspaper, the information was attributed to "one knowledgeable Republican source."

There were other seemingly more important reasons to feel that Throat was not harbored in the FBI. Information he gave Woodward did not always agree with FBI reports. One instance that stood out was that Throat had been quoted as telling Woodward: "You can safely say that 50 people worked for the White House and CRP (Nixon's re-election committee) to play games and sabotage and gather intelligence." It's all in the files, Deep Throat said; "Justice and the Bureau know about it."

The Post story of October 10, 1972, that resulted from the conversation, stated that "according to FBI reports, at least 50 undercover Nixon operatives traveled throughout the country." Students located an FBI report written the day the Post story was published that stated the FBI did not have such information in its files and furthermore it was not true.

Examination of Throat's words and the newspaper stories that resulted shows that much of the information was far removed from the FBI, and instead was White House insider information. An example in our study concerned the knowledge that John Ehrlichman, assistant to Nixon, told E. Howard Hunt, a leader of the Watergate burglars, to get out of town. John Dean, Nixon's chief counsel, testified that Ehrlichman gave that order and told Gordon Liddy, who passed the order to Hunt. Charles Colson, special counsel to Nixon, learned it from Dean and told Dean to rescind the order. But Liddy, Hunt and Colson wrote that they only knew it came from Dean and not from Ehrlichman, and Ehrlichman denied it. Dean said he never told anyone. The only other person believed to have knowledge of Dean's version was Fred Fielding, his chief deputy, who Colson said was present when he talked about it with Dean. We found no mention of the subject in any of the 16,000 pages of FBI reports we examined.

After the announcement that Throat was Felt, it was widely reported that Felt quit smoking in the 1940s. We did not know that because we only went into that much detail when we probed White House suspects. Unlike Felt, our choice for Deep Throat smoked and was in the White House during the entire time when Woodward was getting information from Throat.

While the facts in our online report have not been found to be in error, the big mistake that negates the study is that we came to the wrong conclusion. We were 100 percent sure that Fielding was Deep Throat, I had said publicly. We were that sure, but we were wrong. Only Woodward and Throat together can make that statement.

Fielding was the last man standing in the process of elimination and we then ticked off a list of Throat's facts and compared them with Fielding's knowledge. Fielding saw FBI reports that Dean was getting from L. Patrick Gray, the acting director of the FBI, and sat in on FBI interviews of White House staff members. He prepared White House staff people for investigator's interviews and in one instance got a full report on what the grand jury was asking.

Most surprising was that Fielding's name was left out of Woodward and Bernstein's stories, and we were able to show that they knew of his involvement.

Fielding at one time said he was out of the country when Deep Throat met with Woodward, but we learned that Woodward had not specifically stated the date of the meeting, and had seemingly written around it to obscure it.

Finally, we recounted a published report in which Fielding stated it was probably true that when he was very ill that he said he was Deep Throat.

Fielding would not be interviewed by us or any of the media concerning our report. He would only deny being Deep Throat. He was correct. He is not Deep Throat.

I immediately accepted that we were wrong when Woodward confirmed that the account in Vanity Fair magazine was true. The media response was overwhelming. My e-mail took about 200 messages the first day, and my voice mail filled to capacity. Some of it was ridicule and insults, but there were some comments of support. The most heartening response was from former students. They found Woodward's statement unbelievable, but I told them it had to be accepted. I was especially grateful to students who were on summer break but volunteered to come to my office and help handle the phone calls.

I promised in my media interviews that our next investigation would be of how we went wrong. We also will look at some of the questions that have arisen, such as did Felt work with other people or were there other independent sources who were as important as Throat.

Did we learn from the experience? We probably learned more from being wrong than if we were right.

He secretly guided Washington Post reporter Bob Woodward as he and his colleague Carl Bernstein pursued the story of the 1972 break-in of the Democratic National Committee's headquarters at the Watergate office buildings and later revelations of the Nixon administration's campaign of spying and sabotage against its perceived political enemies.

Felt insisted on remaining completely anonymous, or on "deep background." A Post editor dubbed him "Deep Throat," a bit of wordplay based on the title of a pornographic movie of the time. The source's existence, but not his identity, became known in Woodward and Bernstein's 1974 book, "All the President's Men," and in the subsequent movie version, in which actor Hal Holbrook played the charismatic but shadowy source.

Felt, a dashing figure with a full head of silver hair, an authoritative bearing and a reputation as a tough taskmaster, adamantly denied over the years he was Deep Throat, even though Nixon suspected him from the start.

"It was not I and it is not I," Felt told Washingtonian magazine in 1974. Five times, Nixon ordered Gray to fire Felt, but Gray, convinced by Felt's denials, never did.

Felt, a master of bureaucratic infighting and misdirection, seized upon a Post story that had not used him as a source. In a bold stroke, he denounced it in an internal memo and ordered an investigation into the leak. "Expedite," he commanded. The next day, in a notation on another memo that passed over his desk, he pointed to a prosecutor as the source of the leak.

"I was impressed. My guy knew his stuff," Woodward wrote in "Secret Man: The Story of Watergate's Deep Throat" (2006). "The memo was an effective cover for him, the very best counterintelligence tradecraft. Not only had he initiated the leak inquiry, but Felt appeared to have discovered the leaker."

It wasn't until May 30, 2005, that Felt's family revealed his identity in an article for Vanity Fair magazine. The article, written by San Francisco lawyer John D. O'Connor, did not make clear why Felt, who was suffering from dementia, admitted his identity after more than 30 years. Woodward confirmed the revelation, and secret was finally out.