A 27-year-old woman was raped Sept. 16 at the Park Regency Apartments complex in the 3100 block of Oak Road, the Contra Costa County Sheriff's Office said.
The rape was not believed to have been related to a rape and two attempted rapes reported at the complex in June, July and August.
Detectives are now looking for a man who reportedly went door-to-door soliciting carpet-cleaning services at the Park Regency and other nearby apartment complexes.
He could have information that would assist with the Sept. 16 case, the sheriff's office said.
"At this point he's not a suspect or a person of interest," sheriff's spokesman Jimmy Lee said. "He's someone we want to talk to."
Lee said the man might have been handing out business cards or pamphlets that could be used to track him down.
The rape suspect reportedly forced his way into the victim's apartment as she was entering it at about 6 p.m. the evening of the attack, the sheriff's office said. He later fled on foot.
The suspect was described as a white man, 6 feet tall, between 20 and 30 years old with a full beard. He was wearing jeans, a short-sleeved shirt and a hooded sweatshirt.
The man investigators are now trying to contact is described as a white man, 6 feet tall, with a medium build. He too had a full beard.
Lee said the sheriff's office doesn't know yet if the man they're looking for was the attacker.
"We're hoping to be able to follow up with him," Lee said.