If anything of consequence occurs in this era of smartphones and multi-G wireless networks, a horde of "citizen journalists" will doubtless be on hand to capture and broadcast the sights and sounds. But of hundreds of witnesses in Dallas's Dealey Plaza on Nov. 22, 1963, only a handful managed to record the biggest news story of a generation: the assassination of President John F. Kennedy.

And of the documents they produced, only one stands out: the Zapruder film.

It's not much: About 6 feet (two meters) of narrow, cellulose material, containing fewer than 500 grainy images and running just 26 seconds long. And yet the home movie that clothier Abraham Zapruder shot with his Bell & Howell camera may be the single most important piece of evidence in perhaps the most argued-about crime in the nation's history.

Zapruder was in a unique position to capture the events that day a half-century ago.

Standing on a 4-foot (1.2-meter)-high concrete pedestal, his receptionist bracing him from behind, the 58-year-old Russian immigrant followed the progress of JFK's Lincoln limousine as it rolled toward him down Elm Street. He thought the popping noises he heard were part of some joke, he later told the Warren Commission, and "then I saw his head opened up."

"I started yelling, `They killed him, they killed him,'" he testified before the investigative panel in July 1964. "I was still shooting the pictures until he got under the underpass - I don't even know how I did it."

Tests showed that the camera - loaded with Double 8-millimeter Kodachrome II color film - recorded at an average speed of 18.3 frames per second. Depending on how much film leader and unexposed black footage are counted, there are either 486 or 487 frames with assassination-related images.

Although there was no sound, the Zapruder film allowed investigators and researchers to establish the interval between gunshots.

Zapruder had the film developed and three copies made - two of which he gave to the Secret Service and FBI.

Richard Stolley, then Pacific bureau editor for Life Magazine, had flown in from Los Angeles and reached Zapruder by phone around 11 p.m. The next morning, he was in Zapruder's office at Jennifer Juniors, Inc., watching the film with two Secret Service agents.

"I have to say, seeing that film and seeing the head shot - the infamous frame 313 - was the most dramatic moment of my career," Stolley recalled in a recent interview. "We all reacted as if we had been simultaneously gut-punched."

Competitors avidly sought the film, too. But in the end, Stolley won out, getting Life the print rights for $50,000. The magazine paid Zapruder another $100,000 the following week for the remaining copyrights.

Aside from some still images, it would be years before the general public saw what Zapruder's camera had captured. (Life even withheld frame 313 "out of deference to the grieving Kennedy family," Stolley has explained.)

In 1969, about a year before his death, Zapruder testified as to the film's authenticity during the New Orleans trial of Clay Shaw, the only person ever prosecuted for the assassination. District Attorney Jim Garrison played the film for the jury 10 times - a scene that formed the dramatic crescendo of Oliver Stone's 1991 film, "JFK."

Most Americans did not see the Zapruder film in motion until March 1975, when ABC News aired a copy during Geraldo Rivera's weekly "Good Night America" show.

The outcry helped spur formation of the House Select Committee on Assassinations, which would famously conclude that the murder was most likely the result of a conspiracy involving multiple shooters.

In April 1975, Time, Inc. transferred the original camera print and copyrights back to the Zapruder family. The National Archives and Records Administration agreed to store the film "as a courtesy."

In 1999, the government agreed to pay Zapruder's family more than $16 million for the film. The Sixth Floor Museum in Dallas owns the copyright.

The original is now housed at the archives' facility in College Park, Maryland, in a cold-storage vault, where conditions are kept at a constant 25 degrees Fahrenheit and 30 percent relative humidity. On Oct. 22, a technician removed the film from its protective can for its first inspection in 11 years.

"The reel is in excellent condition, has retained the vivid color typical of Kodachrome, and does not exhibit signs of physical deterioration," NARA spokeswoman Miriam Kleiman wrote in an email to The Associated Press.

On Oct. 15, Life released a new book, "The Day Kennedy Died." In its pages for the first time, each of the frames is shown, in order.

In so many ways, the Zapruder film is a relic, says the 84-year-old Stolley, who shared his recollections in the book. If he were dispatched to Dallas today, he says, "I'd be a little nonplused about who do you negotiate with."

"I mean, in effect," he says, "there would be NO Zapruder film today."