This image from video provided by the Los Angeles County Sheriff's Department shows a suspect officials say is accused of raping a mentally disabled woman on a city bus. Police say the suspect boarded the bus with the woman in Culver City, followed her to the back of the bus and forced himself on her late Wednesday, Nov. 7, 2012. A lone witness tried to alert the bus driver that the rape was happening, but it continued for about 10 minutes until the suspect stopped and exited the bus. (AP Photo/Los Angeles County Sheriff's Department)GREG RISLING
LOS ANGELES (AP) - A man was arrested Friday in the rape of a mentally disabled woman aboard a near-empty Los Angeles County bus during rush-hour commute.
Authorities believe Kerry Trotter, 20, boarded the bus with the 18-year-old woman on Wednesday at a stop in suburban Culver City before she was followed to the back of the vehicle and assaulted.
A witness - the only other passenger on board - tried to alert the driver but was unsuccessful, sheriff's officials said without elaborating.
It was the third rape so far this year on county buses that annually carry millions of people.
"This is an extremely rare occurrence," said Marc Littman, a spokesman for the Metropolitan Transportation Authority.
Trotter was booked for investigation of rape, authorities said. It wasn't immediately known if he had retained an attorney.
Los Angeles County sheriff's investigators said they received an anonymous tip that led to Trotter's arrest after an image of the suspect taken by a surveillance camera on the bus was publicly released.
The attack lasted about 10 minutes before the man stopped and exited the bus, authorities said. After the assault, the woman, who has the mental capacity of a 10-year-old, reported it to the driver who notified authorities, sheriff's Sgt. Dan Scott said.
Authorities have not yet located the lone person who witnessed the rape. Scott would not say if investigators found DNA evidence.
Bus drivers are trained to call transit dispatchers when they become aware of a possible crime, Littman said. If a crime is in progress, there is a silent alarm on board that can be tripped, he said.
It was unclear if the driver saw what transpired. He was being interviewed by authorities.
"We want to see if protocol was followed as well," Littman said.