In the latest incident near Aliso and Alameda streets, a 51-year-old U.S. attorney was punched in the jaw and his head hit a wall.
The same man is believed to be responsible for two other attacks. Police say this could be a copycat crime of the so-called "Civic Center Slapper."
Last month, Jermaine Vincent Moran was arrested and accused of carrying out similar crimes in the same area. Moran allegedly attacked four people.
Police say Moran remains in jail, but the new suspect is at large. He was described as a black man, about 6 feet, medium build and wearing a white knit cap and a white sweater.
Anyone with information is asked to call Crimestoppers at (800) 222- TIPS.