The memo of Bob Bennett's C.I.A. case officer points almost overwhelmingly to Bennett as Deep Throat, the phantom source for Woodward and Bernstein. In that CIA memo it states that Bennett is feeding information to Woodward for which the reporter is 'suitably grateful'.

'Suitably grateful' of course, implies that Woodward is protecting the CIA in exchange for the information. And, in fact, an, examination of Woodward and Bernstein's book, All the President's Men, shows a remarkable coincidence. The CIA is barely mentioned, even-though Woodward admits his first interest in the case came when he heard McCord, at the precinct station, say he had been employed by the CIA

Strange. Nevertheless Woodward has denied that Bennett is Deep Throat. I agree with him. I have my own candidate, based on my knowledge of what was going on at the time Deep Throat was feeding Woodward his stories. Nixon has this same knowledge, too, and from time to time he swings away from Bennett and points to my candidate. His name is Fred Fielding. He was John Dean's staff assistant; a shy, slightly prissy fellow.

Why do I think Fielding is Deep Throat?

1. I begin by accepting Woodward's own description of Deep Throat as a "source in the Executive Branch who had access to information at C.R.P. as well as the White, House." That, if true, eliminates Bennett, who was not in the Executive Branch. Woodward later said in the book that Deep Throat also had special access to the Justice Department and the F.B.I. Only Dean, or his associate, had access from the White House to CRP, the FBI . and the Justice Department during Watergate.

2. The second fact that makes me suspect Fielding is that Dean told us he personally had kept Fielding "out of things" during Watergate. If that's true, you had a man with access to a lot of information from different sources but kept away from other vital information. And that accounts for a mystifying aspect of Deep Throat's behaviour that has gained little or no notice. Not what he told Woodward that was accurate - but what he told Woodward that was wrong and almost every White House staffer knew was wrong. This could only happen if Deep Throat had access to much information, but was deliberately kept "out of things", as Dean had said. Fielding would then let his imagination fill in the gaps.

Shortly after assuming his position, John Dean began thinking about expanding his domain, and hired former Army officer Fred F. Fielding as an assistant lawyer in the counsel's office. They became close friends. In Dean's 1976 memoir, Blind Ambition, he recounted how he explained to his new associate the way in which their careers could quickly rise: "Fred, I think we have to look at our office as a small law firm.... We have to build our practice like any other law firm. Our principal client, of course, is the president. But to convince the president we're not just the only law office in town, but the best, we've got to convince a lot of other people first." Especially Haldeman and Ehrlichman.

But how to convince them? As Dean tried to assess the situation at the White House, events soon showed him that intelligence gathering was the key to power in the Nixon White House. One of Dean's first assignments from Haldeman was to look over a startling proposal to revamp the government's domestic intelligence operations in order to neutralize radical groups such as the Black Panthers and the Weathermen.

The scheme had been the work of another of the White House's bright young stalwarts, Nixon aide Tom Charles Huston. The impetus was a meeting chaired by Nixon in the Oval Office on June 5, 1970, attended by J. Edgar Hoover, Richard Helms, and the chiefs of the NSA and the Defense Intelligence Agency (DIA). The various agencies were almost at war with one another; just a few months earlier, for instance, Hoover had cut all FBI communication with the CIA. Nixon wanted the agencies to work together against the threat from the "New Left." In the aftermath of Nixon's decision in May 1970 to invade Cambodia, and the killings of several students at Kent State University, colleges all over the country were again being rocked by riots and demonstrations as they had been in the last year of Lyndon Johnson's presidency, and for the same reason-young people were objecting to the president's war policies. In Nixon's view, the threat was grave and must be attacked; therefore the agencies must find some way to bury their differences and concentrate on the true enemy. Huston was assigned to help Hoover and the intelligence chiefs clear obstacles to their working jointly on these matters.

In early July, Huston sent a long analysis to the president, endorsed by Hoover and the other intelligence agency directors, on how to enhance cooperation. To this memo Huston added his own secret one that became known as the "Huston Plan." It called for six activities, some of which were clearly illegal. They included electronic surveillance of persons and groups "who pose a major threat to internal security"; monitoring of American citizens by international communications facilities; the relaxation of restrictions on the covert opening of mail by federal agents; surreptitious entries and burglaries to gain information on the groups; the recruitment of more campus informants; and, to ensure that the objectives were carried out and that intelligence continued to be gathered, the formation of a new interagency group consisting of the agencies at the June 5 meeting and military counter-intelligence agencies. Nixon endorsed these measures in the Huston Plan on July 14, 1970, because, as he put it in his memoir, "I felt they were necessary and justified by the violence we faced."

The secret plan angered J. Edgar Hoover, not because he objected to coming down hard on dissidents, but, rather, because he felt that any new interagency group would encroach on the turf of the FBI and because he was concerned about the negative public reaction should any of the activities be exposed. On July 27, the day Dean began work at the White House, Hoover took the unusual step of venturing out of his own domain to visit his nominal superior, Attorney General John Mitchell. As Hoover learned, Mitchell did not know anything about the Huston Plan at the time. "I was kept in the dark until I found out about it from Hoover," Mitchell later told us. But as soon as he was apprised of the plan, Mitchell agreed with Hoover that it must be stopped-not for Hoover's reasons, but because it contained clearly unconstitutional elements-and immediately visited Nixon and told him it could not go forward. In testament to Mitchell's arguments and good sense, Nixon canceled the plan shortly thereafter and Huston was relieved of his responsibilities in the area of domestic intelligence.

Coordination of official domestic intelligence from various federal agencies concerning anti-war activists and other "radicals" was then handed to the new White House counsel, John Dean, along with a copy of the rejected Huston Plan. But it seemed that the president was still not satisfied with the quality of domestic intelligence, because in August and September Haldeman pushed Dean to try and find a way around the Hoover road-block. In pursuit of a solution, on September 17, 1970, Dean went to see his old boss, John Mitchell. Hours earlier, Mitchell had lunched with Director Helms and other senior CIA officials who had all agreed that the FBI wasn't doing a very good job of collecting domestic intelligence.

Dean and Mitchell spoke, and the next day Dean prepared a memo to Mitchell with several suggestions: "There should be a new committee set up, an interagency group to evaluate the government's domestic intelligence product, and it should have "operational" responsibilities as well. Both men, Dean's memo said, had agreed that "it would be inappropriate to have any blanket removal of restrictions" such as had been proposed in the Huston Plan; instead, Dean suggested that "The most appropriate procedure would be to decide on the type of intelligence we need, based on an assessment of the recommendations of this unit, and then to proceed to remove the restraints as necessary to obtain such intelligence."

Dean's plan languished and was never put into operation. Years later, in the spring of 1973, when Dean was talking to federal prosecutors and preparing to appear before the Senate committee investigating Watergate, he gave a copy of the Huston Plan to Federal Judge John J. Sirica, who turned it over to the Senate committee. Dean's action helped to establish his bona fides as the accuser of the president and was the cause of much alarm. In his testimony and writings thereafter, Dean suggested that he had always been nervous about the Huston Plan and that he had tried to get around it, and as a last resort had gotten John Mitchell to kill the revised version. In an interview, Dean told us, "I looked at that goddamn Tom Huston report," went to Mitchell and said, "General, I find it pretty spooky." But as the September 18, 1970, memo to Mitchell shows, Dean actually embraced rather than rejected the removal of "restraints as necessary to obtain" intelligence.

A small matter? A minor divergence between two versions of the same incident? As will become clear as this inquiry continues, Dean's attempt to gloss over the actual disposition of the Huston Plan was a first sign of the construction of a grand edifice of deceit.

Bob Haldeman's book about Watergate, The Ends of Power, named Fred Fielding as Deep Throat. I felt I should do something.

Fred Fielding had been more than my deputy at the Nixon White House, he'd been one of my closest friends. We'd shared good times and tough times, and, when Watergate became a part of my daily life at the White House, it had strained both our friendship and working relationship. At first I had talked openly with Fred about Watergate, and we'd worked on it together, as we did so many matters that came through our office. However, when I realized the direction Watergate was headed, I stopped talking with Fred. From the day I was asked to find out about raising hush money for the men arrested at the Watergate complex, I knew the cover-up was headed toward criminal activity. There was no reason to draw Fred into the mess I'd found myself a part of.

At the time, Fred was annoyed and upset with me. Later, when he realized I had protected him and the others on my staff-from the facts of Watergate, he was appreciative. I knew Fred had not had it easy in convincing investigators and reporters that he knew nothing, but I knew he knew nothing about Watergate. And I was sure that the name Deep Throat, courtesy of Bob Haldeman, would be a most unwelcome appellation, since it all but made Fred a liar. I called Fred to talk with him about how he was going to deal with the situation.

Fred said he had learned several weeks before publication that Haldeman had named him Deep Throat. "An old friend, a reporter, called me," Fred explained. "He'd seen an advance copy and wanted to know if I'd give an exclusive interview I was quite taken aback by the whole thing."

I asked why he thought Haldeman had named him.

"I've got no idea why he'd name me." And then, with the old Fielding wit, he added, "Everybody in the world knows it was Hal Holbrook."

Fred explained what I knew well, that he didn't have access to the information that Deep Throat possessed; however, he felt he had something even more important going for him: "I'm fortunate that I've got evidence that'll show I couldn't be Deep Throat. When I learned what Haldeman had done, I reread Woodward's book, and one of the most critical conversations he had with Deep Throat was on January 24, 1973. As it happened, you'll recall, I was out of the country, in South America on government business, from about the 22nd of January until the 27th or 28th. I've been looking for my old passport, which will have the evidence stamped right on it."

We talked about how he'd proceed if and when he located his passport. I suggested he take it over to Hays Gorey, at Time magazine. I told him Hays had had a continuing interest in the Deep Throat story and, if he could prove it to Hays, Time magazine would certainly shoot down the Haldeman allegation. Fred agreed.

Understandably, Fred was angry with Haldeman's dragging him back into Watergate. "And another thing about his book that I guess I shouldn't be surprised about, but I was," Fred noted, "is that he has nothing good to say, nothing positive to offer, about anyone he discusses-except himself." Somewhat bitterly, Fred observed, "Haldeman may have made his mark in history, but it certainly isn't as a historian."

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.

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.