REDWOOD CITY -- A 52-year-old San Francisco man described as a "career flasher" by prosecutors was sentenced Wednesday in San Mateo County Superior Court to 13 years in prison for exposing himself to a woman on a Bay Area Rapid Transit train in 2006.

Kenneth Ray Burton was arrested by BART police July 15, 2006, after masturbating in front of a woman in her 30s on a train traveling from San Francisco to Millbrae, according to Chief Deputy District Attorney Steve Wagstaffe.

Burton pleaded no contest Aug. 2 to five counts of felony indecent exposure. He was charged with four extra counts for other victims who left and moved to adjacent cars, leaving the woman alone in the car with Burton, Wagstaffe said.

Burton was charged with sexual assault about 25 years ago, and since then has had two indecent exposure convictions, according to Wagstaffe.

"He's a career flasher," Wagstaffe said, adding that psychiatrists have determined he now poses little threat of sexual assault, but has "an uncontrollable predilection to expose himself to women," he said.

Because of the prior strike convictions, Burton's sentence today totaled 13 years and four months in state prison.