Kenneth Hoyt, a sex offender who's done time in three states, flashed women on the R train, police said. View Full Caption NYPD and the Division of Criminal Justice Services

MANHATTAN — A sex offender, who's been in and out of prison in three different states since the 1980s, turned himself in Monday to federal authorities for flashing women on the R train and groping others on the subway, NYPD officials said.

Kenneth Hoyt, 52, flashed three women on R trains in August and September, officials said Thursday.

Hoyt, reportedly a onetime porn actor, was brazenly riding the rails wearing only a long camouflage shirt, officials said.

Hoyt, who was out of federal prison on supervised release, turned himself at a probation hearing Monday about 5 p.m., an NYPD spokeswoman said.

Hoyt, whose address is listed as the Kirby Forensic Psychiatric Center on the sex offender registry, is awaiting formal charges for flashing subway riders. He's also expected to be charged with groping other straphangers, but officials didn't have further details about that.

Hoyt's history is riddled with sex offenses stretching back four decades and over three states, records show.

Hoyt was adopted by an engineer and and a teacher, a charitable Christian couple, the year he was born, records show.

Hoyt, who grew up with a brother and sister, liked skateboarding, swimming and music, his mother, Betty Hoyt, wrote to a federal judge in 2013.

"Ken is a talker, loves to read self-improvement books (e.g. health, finance, nutrition), likes to work out every day, and keeps busy by staying active," his mother wrote.

"Kenneth has always been a peaceful person [who] tends to support 'the underdog' as a child he stood up to bullies," she added.

His mother, who was 86 at the time, wrote to Judge Robert Sweet to convince him to give Hoyt a lenient sentence for failing to register as a sex offender in New York when he moved there from California.

"In the brief time I have remaining, I would like an opportunity, as soon as possible, to once again share a household with Kenneth, for the opportunity to exert my influence in re-directing every portion of his life to bring an upright citizen in every regard, to reinforce the fine qualities he already has, and to re-assure him he has a future with hope," the elder Hoyt wrote.

"Ken has shared his regrets about actions that have gotten him into trouble," she added.

Hoyt was first arrested in 1984 when he was 19 for making harassing phone calls in Orange County, California, records show.

A year later, he was convicted for molesting a 13-year-old girl, records show.

Once out on parole, he then exposed his buttocks to two 16-year-old girls in Las Vegas in 1990, records show.

He was arrested again in December 1991 just after his release for making obscene phone calls to girls and exposing himself in Las Vegas, records show.

"The defendant had five female juveniles inside his apartment who were all partially undressed. Two of the girls told police that the defendant had offered them $75 each to strip for him, and $75 to another girl if she would have sexual intercourse with him," federal prosecutors said.

He served his time in Vegas before moving to New York in 2002 only to get arrested on prostitution charges a year later, records show.

While flashing a 25-year-old woman on a Manhattan R train in 2006 he wore a jacket emblazoned with his personal porn website, which she used to tip off police, the Daily News reported.

Hoyt was arrested again in 2007 for a slew of subway sex crimes — including masturbating in front of 16-year-old girls — only to have those charges dropped because an ADA filed required paperwork four days after its deadline, according to records and the New York Post.

Hoyt moved back to Los Angeles and was arrested for failing to register as a sex offender there in 2009, records show.

Hoyt pleaded guilty, but while waiting for his sentence, he was arrested again for exposing himself in March, records show. He had been masturbating in his car in a Chevron gas station and then followed a UCLA student who spotted him, the university reported.

Hoyt was released from prison in June 2012 and issued a GPS monitoring bracelet, which he cut off on Oct. 11, 2012, before fleeing to New York, prosecutors said.

That Halloween, he moved into an Upper West Side apartment of a family with a 6-year-old girl, records show. It wasn't immediately clear if the family knew about Hoyt's past.

Authorities tracked him down in January 2013 when he put an ad on Craigslist offering to share the room in the Upper West Side apartment he was subletting, records show. He dubbed himself "Kenny" in the listing and listed his phone number.

That phone number was also posted on massagem4m.com advertising the services of a masseur named "Mario," prosecutors said. Undercover agents booked a reservation with the masseur and arrested him in a Upper East Side hotel when they realized it was Hoyt, records show.

He was convicted of failing to register as a sex offender in New York and sentenced to 30 months in prison on Nov. 7, 2013, with a decade of supervised release thereafter, records show.