50 years ago, he saw a document in the JFK file. Where is it now?

In March 1976, a young Senate staffer named James Johnston who was investigating the assassination of President John F. Kennedy was summoned to CIA headquarters to meet an unidentified agency representative. The man showed him an explosive document whose existence has never been revealed publicly — until now.

The document said that “the Mexican government had investigated Kennedy’s assassination and concluded Cuba was responsible,” recalls Johnston, a lawyer and writer who has closely followed the assassination ever since. According to a vetting slip he saw that day, Johnston told me, this file had only been read by five other people, one of whom was Richard Helms, who headed the CIA from 1966 to 1973.