According to director Don Siegel, star Eli Wallach was originally hostile because he was upset that, after a prestigious film debut in Baby Doll, he was doing a routine thriller as his second film. Midway through the shoot, however, Wallach realized he was actually playing a complex role in a well-written film and became more sympathetic to the project.
The scene in which the car nearly drives off the end of San Francisco's unfinished Embarcadero Freeway, before the driver swerves just in time, was done by stunt driver Guy Way. Way had his wife with him when he did the stunt, and she freaked out and didn't recover for several days.