Although the production crew had no permits, the scenes showing the deserted city were filmed in downtown Los Angeles on Sunday mornings when the streets would be vacant.
Only one robot costume was constructed for this film and it was used for all robot scenes. This is why you never see more than one member of the "robot army" in a shot.
The killer, (played by Robert Roark) got his part because his father, a doctor in LA would invest in the film if his son was given a part. After this part he went on to play in many movies and became a producer.