And then there's the testimony of Julia Ann Mercer, the wife of a U.S. Congressman. Like many witnesses, Mrs. Mercer later discovered that the FBI had brazenly misrepresented what she had said during her FBI interview. Mrs. Mercer corrected the FBI's distortion when she spoke with Jim Garrison's staff. At first, Garrison didn't believe her because, at that point, he didn't believe that FBI agents would misreport an interview and forge a signature, but Mrs. Mercer and her husband proved that the signature on the FBI interview report was not hers.
Mercer said she saw Jack Ruby driving a truck in Dealey Plaza about 90 minutes before the assassination, and that another man exited the back of the truck carrying what appeared to be a rifle case, walked up the grassy knoll, and did not return to the truck.
This is essentially the same account that she gave to the Dallas County Sheriff's Department shortly after the assassination. She didn't mention Jack Ruby because she didn't know who he was at that point. She mentioned the truck and mentioned seeing a man carrying a gun case get out of the truck and walk up the grassy knoll.
In her discussion with Garrison staffers, Mrs. Mercer related the following:
On Saturday 23 November, she had positively identified a photograph as that of the man in the driver’s seat of the pick–up truck. She had turned the photograph over and saw Jack Ruby’s name written on the back.
After seeing Ruby murder Oswald on television, she contacted the FBI and told them that Ruby had been the man sitting in the pick–up.