The car chase was filmed in two days without permits using rented automobiles from Hertz.
The sequence with Hank McCain being released from jail was shot at San Quentin Prison without permits.
The first collaboration between John Cassavetes and Peter Falk, who would have a fruitful creative partnership in the 1970s. Ironically, the two do not share any scenes together.
McCain's eponymous submachine gun is a STEN Mk II. The weapon was manufactured for the British military during World War II as a cheap, easily mass-produced light infantry gun that was primarily utilized by insurgent forces.