During location filming in Washington, DC, Martin Luther King was assassinated. The resulting riots in the capital caused the shooting company to wrap early and return to Los Angeles. Visible in the rear window of the cab during Jean Seberg's ride through the city, buildings are burning and smoke is obvious.
In the Matthews' bedroom there is a photograph of Jean Seberg on the dresser, which is actually a publicity still from Lilith (1964).
The audio for the voice of Senator Augustus Cole, played by Paul McGrath, had to be re-recorded by another actor after it was found street noise spoiled the shot. By the time the studio was ready for "looping," McGrath was nearly unavailable. In Summer 1968, McGrath was touring the Northeast U.S. on a summer theater gig, supporting Shirley Booth in The Desk Set, and he had only Sundays off, as those were travel days. Since George Peppard refused to work Sundays, Les Tremayne was commissioned to do the job as a voice-over. Source: Column by Hobe Morrison, The Herald-News (Passaic, NJ), March 31, 1969.
Dana Elcar plays Police Det. J.J. "Red" Thornton. Elcar went on to play another character named Thornton in the TV series MacGyver, one of his best-known roles.
Despite her fame and prominent billing, Jean Seberg has only a small role in the film and her character is killed off less than half way through.