There the Easy Rider actor, 70, came upon a grim scene: A dead body slumped over the wheel of a sedan.
"He looked in the vehicle and saw a body in there and called the fire department," Los Angeles Police Homicide Detective Allen Shubert told CNN.
The body turned out to be that of a man in his 50s who had committed suicide days before, Shubert said.
Fonda is best known as the star of 1969's Easy Rider, and is the son of Henry Fonda and the brother of Jane Fonda.
The deceased man's identity has not been released.