Click photo to enlarge
**FILE** The Park Regency Apartments in Walnut Creek, Calif., Friday, Sept. 17, 2010, a day after a woman was sexually assaulted at the apartments. (Dan Rosenstrauch/Staff)

A tenant of the Park Regency Apartments near Walnut Creek has been arrested and charged in the September rape and assault of a woman living at the complex, the Contra Costa County Sheriff's Office announced Friday.

Investigators say 51-year-old William Yokeum committed only the fourth of the five assaults that have occurred at the apartments at 3128 Oak Road since late June. Another man was arrested in connection with the first three incidents and investigators are searching for a suspect in the most recent assault, Oct. 2.

Unlike the first three assaults, which authorities believe were committed by a stranger, Yokeum knew the woman he is alleged to have raped Sept. 16 at the complex where he lives, sheriff's spokesman Jimmy Lee said. Yokeum and the victim had met previously.

Investigators said he forced his way into the 27-year-old woman's apartment as she was returning home.

Initially, the investigation focused on a man who was going door-to-door offering carpet-cleaning services. Lee said that turned out to be a false lead.

Yokeum was arrested Wednesday and formally charged Friday with rape, sodomy, oral copulation, penetration with a foreign object and burglary.

He is being held at the Contra Costa County Jail in Martinez with bail set at $1.6 million.

Several residents refused to comment Friday night and a security guard there said management had issued instructions not to let members of the media on the property.

One female resident who did not want to give her name said she had not heard about Yokeum's arrest, but did feel somewhat safer.

"I feel that there's still sick men that do copycat crimes," she said, adding that she believes there is still too much access to walk-in traffic despite recent efforts to increase security.

"I definitely feel that they need more than two security people at the main entrance."

Two private security guards were stationed there Friday, as well as a sheriff's patrol car.

Lee said the added sheriff's presence has been in place since the beginning of the month.

"We have increased our security around the complex, and not just the apartment complex, but the entire Contra Costa Centre," Lee said.

The first three attacks at Park Regency occurred from June 30 to Aug. 10. In August, authorities arrested 22-year-old Antonio Mouton, of Berkeley, and charged him with raping one woman and assaulting two others.

In the Oct. 2 attack, a 43-year-old woman was walking in an open-air hallway outside her apartment when a man grabbed her and tried to force her into her apartment.

The woman fought off the attacker and ran away, but fell down stairs and injured her back and leg.

The suspect involved in that assault was a white man between 5 feet 8 and 5 feet 9 with a medium build, brown hair and facial hair. He was wearing black jeans, a black T-shirt and a black baseball cap.

Anyone with information on the crime or the attacker can call the Sheriff's Office at 925-313-2620.

Roman Gokhman covers public safety. Contact him at 925-945-4780. Follow him at Twitter.com/romithewriter.