In an upcoming memoir, 88-year-old former Secret Service agent Paul Landis says he took a bullet from the car after Mr Kennedy was shot and left it on his stretcher.

For those who have spent decades scrutinizing every shred of evidence in a case that has been investigated since the 1960s, Mr Landis’s account is a major and unexpected development. Since the assassination, conspiracy theories have abounded regarding how many gunmen were involved, who was ultimately responsible, and how many bullets struck the president..