Jack Lawrence worked for the Downtown Lincoln-Mercury car dealership in Dallas. Lawrence claimed that Lee Harvey Oswald asked to test-drive a car in early November. Afterwards Lawrence reported the incident to the Federal Bureau of Investigation.

On 21st November, 1963, Lawrence borrowed one of the firm's cars. The following day he failed to turn up for work. According to Jim Marrs (Crossfire): "about thirty minutes after the assassination, he came hustling through the company's show room, pale and sweating with mud on his clothes. He rushed into the men's room and threw up. He told co-workers he had been ill that morning, and that he had tried to drive the car back to the dealership but had to park it due to the heavy traffic. Later, employees found the car parked behind the wooden picket fence on top of the Grassy Knoll overlooking Dealey Plaza."

Lawrence's strange behaviour was reported to the Dallas police. He was interviewed by officers investigating the assassination of John F. Kennedy. They discovered that Lawrence was a marksman in the United States Air Force.

According to Beverly Oliver, Lawrence was a regular at the Carousel Club (owned by Jack Ruby) and a close friend of George Senator.