In October 1961, Mary began visiting John F. Kennedy in the White House. It was about this time she began an affair with the president. Mary told her friends, Ann and James Truitt, that she was keeping a diary about the relationship.In 1962 Mary made contact with Timothy Leary, the director of research projects at Harvard University. Leary supplied LSD to Mary who used it with Kennedy. Leary also claimed that Mary helped influence Kennedy's views on nuclear disarmament and rapprochement with Cuba. It was later discovered that the FBI was keeping a file on Mary. Later, James Angleton, head of counterintelligence at the CIA admitted that the agency was bugging Mary's telephone and bedroom during this period.
Kennedy aide, Meyer Feldman, claimed in an interview with Nina Burleigh that the president might have discussed substantial issues with her: "I think he might have thought more of her than some of the other women and discussed things that were on his mind, not just social gossip."
http://www.spartacus.schoolnet.co.uk/JFKmeyerM.htm
On 12th October, 1964, Mary Pinchot Meyer was shot dead as she walked along the Chesapeake and Ohio towpath in Georgetown. Henry Wiggins, a car mechanic, was working on a vehicle on Canal Road, when he heard a woman shout out: "Someone help me, someone help me". He then heard two gunshots. Wiggins ran to the edge of the wall overlooking the tow path. He later told police he saw "a black man in a light jacket, dark slacks, and a dark cap standing over the body of a white woman."
