Fifty years ago on November 22, 1963, in Dallas' Dealey Plaza, John Fitzgerald Kennedy, the 35th President of the United States, was assassinated while travelling in a motorcade with his wife, Jacqueline. LIFE magazine, the weekly pictorial chronicle of events in America and throughout the world, was quickly on the scene. The Kennedys had been our story: Jack and Jackie made the cover in his sailboat before they were married and he was a fresh-faced senator from Massachusetts, and the White House doors had remained open to LIFE throughout his presidency: Cecil Stoughton's photographs of Caroline and John - John in the Oval Office, Jackie's tour of the renovation, tense behind-the-scenes moments during 13 days of the Cuban Missile Crisis - all of this appeared in LIFE. We needed to be in Dallas. The famous Zapruder film first appeared in LIFE, after being acquired by LIFE's Richard B. Stolley. Stolley also interviewed at the time Dallas police, Kennedy administration officials, members of the Oswald family, workers at Jack Ruby's bar. Jackie's first conversation after the murder was with Theodore H. White for LIFE, and in it she told the American people, for the first time, about the Camelot her late husband had imagined. All of that is revisited in this commemorative book, including the publication of never-before-seen photography as well as a complete reprint of our 1963 special edition on the events in Dallas. But also: In an extended essay, Dick Stolley remembers the time, and goes back to sources that are still living. Images from the Zapruder film are reprinted and assessed 50 years later. Alexandra Zapruder writes exclusively for LIFE about her experiences and those of her family. J.I. Baker, author of The Empty Glass, about the death of Marilyn Monroe, analyzes a half century of conspiracy theories (80 percent of Americans believe JFK was the victim of a conspiracy) exclusively for this LIFE book. And LIFE talks with not only Kennedy associates but a host of other Americans, asking the question: Where were you when you heard?