A man arrested Sunday in the case of a 16-year-old at-risk girl who walked away from an Oakland group home has been charged with kidnapping her, holding her in his San Francisco home and raping her repeatedly, authorities announced Tuesday.

Gary Steven Atkinson, 36, was arraigned today on charges of kidnapping, three counts of rape of an incompetent person, three counts of lewd acts upon a child, and one count of an attempted lewd act upon a child, according to the Alameda County District Attorney's Office.

"This is by far one of the most sickening cases I've seen in my career -- to take advantage of someone of this stature," Oakland police Chief Howard Jordan said at a news conference Tuesday.

The girl, who is autistic, walked away from the Fred Finch Youth Center at 3800 Coolidge Ave. on the night of Nov. 27.

She was followed by staff until they lost sight of her near the corner of 34th Avenue and International Boulevard, near the Fruitvale BART station. The staff then alerted police that she was missing.

Police said the girl has the mental capacity of a 9- to 12-year-old.

According to a probable cause statement filed with the district attorney's office by Oakland police Officer Alonzo Weatherly, the girl was kidnapped near the BART station and taken to a residence in San Francisco where she was held and raped multiple times over a three-day period before she managed to escape.

A San Francisco Municipal Railway train operator found her Thursday night, "disoriented and very scared," Oakland police Lt. LeRonne Armstrong said Tuesday.

But the girl was also "resilient" and managed to assist investigators in finding her attacker, Armstrong said.

Police distributed a photo of the suspect obtained from surveillance cameras at the Fruitvale BART station, and arrested Atkinson at about 9 p.m. Sunday near the corner of 34th Avenue and International

Boulevard, near where the alleged kidnapping occurred.

Atkinson has previously been convicted of several felonies, including burglary, robbery and assault with a deadly weapon. He is due back in court Wednesday.

The California Department of Social Services, which oversees centers for developmentally disabled children, is investigating the incident to determine if Fred Finch officials acted appropriately, spokesman Michael Weston said Monday.

He said that if the investigation determines that the youth center didn't handle the situation properly, it could face a wide variety of sanctions, up to having its license revoked.

He said federal law requires that licensed care homes keep their doors unlocked, and prevents them from restraining residents to keep them from leaving.

Weston said that if a child tries to leave a facility, staff members should try to redirect them to stay but can't block them from leaving.

He said staff members are directed to follow any youth who leaves and then contact police if they appear to be in danger.