Forty years later, suspicions of a conspiracy endure: Seven in 10 Americans think the assassination of John F. Kennedy was the result of a plot, not the act of a lone killer — and a bare majority thinks that plot included a second shooter on Dealey Plaza.

ABCNEWS has completed a poll in conjunction with a two-hour ABCNEWS special, Peter Jennings Reporting: The Kennedy Assassination — Beyond Conspiracy, airing 9-11 p.m. (EST) Thursday, Nov. 20. The program includes a computer-generated reconstruction of the shooting that confirms that Oswald was the lone gunman. And it finds no persuasive evidence of a conspiracy to kill the president.

Just 32 percent accept the Warren Commission's 1964 finding that Lee Harvey Oswald acted alone when he shot Kennedy as his motorcade passed through downtown Dallas on Nov. 22, 1963. Fifty-one percent think there was a second gunman, and seven percent go so far as to think Oswald wasn't involved at all.

Sixty-eight percent of Americans also think there was "an official cover-up" to hide the truth about the assassination from the public. And about as many, 65 percent, think that "important unanswered questions" remain, four decades after Kennedy's death.

While such suspicions are well-documented - and well-stoked by conspiracy theorists - for many people they're guesses, not convictions. In a new follow-up question, fewer than half of Americans, four in 10, say they're "pretty sure" there was a plot; another three in 10 say it's just a hunch. Similarly, half of those who suspect a second shooter say this, too, is just their hunch.

Suspicion has been long-running; as far back as 1966, a Harris poll found that 46 percent of Americans thought there was a "broader plot" in the assassination. This jumped to 60 percent in 1967, after New Orleans District Attorney Jim Garrison filed charges alleging a conspiracy (the man he charged, Clay Shaw, was acquitted in 1969).

Belief in a broader plot peaked at 80 percent in a 1983 ABCNEWS poll; it's since eased a bit, to today's 70 percent. Similarly, the number of people who think there was an official cover-up has moved back from its peak, 81 percent in 1993, to 68 percent now.

No other murder in history has produced as much speculation as that of President John F. Kennedy. Forty years after he was fatally shot, more than 80 percent of Americans still believe there was a conspiracy to kill the president and that the assassin, Lee Harvey Oswald, did not act alone. After a thorough investigation, including more than 70 interviews, ABCNEWS has produced a two-hour special that separates facts from conspiracy theories and gets to the truth. The special aired on Thursday, Nov. 20th 2003, two days before the 40th anniversary of the Kennedy assassination. "There has been so much innuendo and presumption in the conspiracy theories, that on this 40th anniversary of the president's murder, the subject cries out for review," said Peter Jennings, who anchors the special. "The truth is knowable." Peter Jennings Reporting: The Kennedy Assassination Beyond Conspiracy showcases intricate forensic technology that makes it possible to be an eyewitness to the crime of the century, allowing viewers to see precisely what happened in Dallas' Dealey Plaza on Nov. 22, 1963. Award-winning animator Dale Myers has spent the last decade creating a three-dimensional, computer-generated reconstruction of the assassination based on maps, blueprints, physical measurements, more than 500 photographs, the Zapruder film, and crime-lab and autopsy reports. His work has been independently evaluated and given the highest marks by the foremost practitioners of this type of forensic analysis. ABCNEWS conducted extensive interviews with friends and family of Oswald and his killer, Jack Ruby; former officials from the CIA, FBI, the Russian KGB and the Dallas Police; important players in the Kennedy and Johnson administrations; and participants in the various official investigations, including the Warren Commission.

It's been 40 years, and still the debate continues. Was Lee Harvey Oswald part of a conspiracy to kill President John F. Kennedy, or did he act alone?

A documentary airing Thursday on ABC, one of several programs this week observing the 40th anniversary of the Kennedy assassination Nov. 22, 1963, claims to offer proof that Oswald was the only gunman.

Will ABC's film, "Peter Jennings Reporting: The Kennedy Assassination – Beyond Conspiracy," resolve all the doubts? Probably not. After all, as Robert Kennedy biographer Evan Thomas observes, Americans want to believe "when something terrible happens in America, there has to be a reason for it. It's not good enough to say some nut with a rifle killed JFK. Such a monstrous thing, there must be a monster plot."

Not necessarily, says computer animator Dale Myers. With his help, ABC's documentary looks at the assassination from a different angle. Literally. Myers, says ABC News anchor Peter Jennings, has been studying the assassination for more than 25 years. Starting with Abraham Zapruder's eight-millimeter home movie of the Dallas shooting, plus maps, measurements, blueprints and more than 500 photographs, he created a computer animation of Kennedy and Texas Gov. John Connally riding in that familiar open convertible. "When all of these elements come together, we can now leave the place where Zapruder was filming," says Jennings, as Zapruder's camera seems to fly across the street, "and see the shooting from any point of view, each an accurate representation of precisely what happened."

Myers plays back the Zapruder film frame by frame, dissolves to his computerized images, and notes that Kennedy and Connally seem to be hit by a bullet at the same instant. He concludes that the first bullet to hit Kennedy "is going to hit Governor Connally exactly where he was hit. The fact that they both react at the same time clinches it. It's not a 'magic bullet' at all. It's not even a single bullet theory at all in my opinion. It's a single bullet fact." Tracing the bullet's path backward, he claims, "you can start with, for instance, with Governor Connally's entrance wound in his back, connect that with the point of exit on the President's throat, take that line and project it rearward. What we end up with is a line that goes right back through the sniper's nest window in the sixth floor of the Texas School Book Depository." That "nest," of course, is where investigators later found three spent shell casings. Executive producer Tom Yellin has said the documentary "leaves no room for doubt" that Oswald acted alone. "It's irrefutable." Jennings notes, by the way, that "If the crime were committed today, forensic investigators would unquestionably use this technique." And if the crime were committed today, there would be dozens, if not hundreds, of home videos of the scenario.