William Yokeum, 51, is a resident at the Park Regency apartment complex, where a 27-year-old woman was sexually assaulted on Sept. 16, the sheriff's office said.
The complex was the site of several other assaults over the summer, but investigators quickly ruled out an association between those incidents and the September attack. An Oct. 2 incident at the Park Regency apartments also does not appear to have been related.
Investigators determined that Yokeum and the Sept. 16 victim knew each other and had contact prior to the assault, the sheriff's office said.
Yokeum was arrested on Wednesday and has been charged with rape, sodomy, oral copulation, penetration with a foreign object, and burglary.
Deputies are still looking for the Oct 2 suspect, who tried unsuccessfully to force his way into a woman's apartment.
Berkeley resident Antonio Mouton, 22, was arrested for a rape and two attempted rapes in June, July and August. He has pleaded not guilty.
Anyone with information about the attacks is asked to call the sheriff's office at (925) 313-2620.