"The day after the assassination, Gary Underhill left Washington in a hurry. Late in the evening he showed up at the home of friends in New Jersey. He was very agitated. A small clique within the CIA was responsible for the assassination, he confided, and he was afraid for his life and probably would have to leave the country. Less than six months later Underhill was found shot to death in his Washington apartment. The coroner ruled it suicide."
[...]
"The friends whom Underhill visited say he was sober but badly shook. They say he attributed the Kennedy murder to a CIA clique which was carrying on a lucrative racket in gun-running, narcotics and other contraband, and manipulating political intrigue to serve its own ends. Kennedy supposedly got wind that something was going on and was killed before he could 'blow the whistle on it.' Although the friends had always known Underhill to be perfectly rational and objective, they at first didn't take his account seriously. 'I think the main reason was,' explains the husband, 'that we couldn't believe that the CIA could contain a corrupt element every bit as ruthless--and more efficient--as the mafia.'
"The verdict of suicide in Underhill's death is by no means convincing. His body was found by a writing collaborator, Asher Baynes of the New Republic. He had been shot behind the left ear, and an automatic pistol was under his left side. Odd, says Brynes, because Underhill was right-handed. Brynes thinks the pistol was fitted with a silencer, and occupants of the apartment building could not recall hearing a shot. Underhill obviously had been dead several days." - [Memorandum, 7/19/1967, SUBJECT: Ramparts: John Garrett Underhill Jr, Samuel George Cummings, and Interarmco]