A handyman at a trailer park in Pennsylvania has been arrested after four decades of allegedly raping and sexually abusing children, including sex acts involving a relative and youngsters he babysat.

William Charles Thomas, 58, of Morrisville, allegedly admitted to the sickening charges last week during interviews with investigators who launched a probe after getting a tip on sexually graphic writings found on a piece of plywood at Midway Village Trailer Park in Morrisville.

Thomas, who worked as a handyman at the trailer park, had been making renovations to the unit when the new owner spotted the handwritten description of “someone sexually assaulting two very young girls,” according to court documents obtained by The Post.

The girls, according to the affidavit of probable cause, were later identified as the daughters of former residents of the trailer park. But when investigators began searching Thomas’ trailer last week, they found an extensive, disturbing collection of evidence, including more than 1,000 images of naked children, up to 1,000 pairs of girls’ underwear – some of which he hung over his bed – dolls that were altered for his sexual gratification and “incredibly vulgar and graphic drawings and writings” chronicling his decades of abuse.

“Some of these writings documented Thomas ‘molesting’ children as young as three years old, when Thomas was in his twenties, which would be during the nineteen seventies, as Thomas also wrote that he was aware some of the children were either asleep or so young that they wouldn’t be able to disclose the abuse,” the document reads.

Thomas told investigators on Feb. 4 that he had been sexually attracted to children since his adolescence and admitted collecting the images of naked children over the course of decades. He also told investigators about sex acts with a relative and abusing two children while bathing them under his care.

Thomas told investigators that while working as a handyman or contractor, he would occasionally steal young girls’ underwear or school pictures from the homes of customers for his sexual gratification.

Bucks County District Attorney Matthew Weintraub detailed the charges against Thomas during a press conference on Monday. He characterized Thomas as a “real life boogeyman” who kept a “perverse shrine” for his decades of stalking children.

“This is a parent’s worst nightmare,” Weintraub said, according to Philly.com.

Thomas previously ran a remodeling business in Falls Township called Thomas Construction. His victims were both male and female and ranged in age from two to 10 years old.

Lt. Henry Ward of the Falls Township Police Department, which took four days to process the droves of evidence found in Thomas’ home, said the victims in the case were “broken.”

“The human race hasn’t come up with words of what we saw in the trailer,” said Ward, who described the scene as “horrific.”

Thomas is charged with five counts of rape involving children under the age of 13, five counts of involuntary deviate sexual intercourse with a child and three counts of aggravated indecent assault of a child. He is scheduled to appear for a preliminary arraignment on those charges early Tuesday.

Thomas was arraigned Friday on charges of possession of child pornography and dissemination of photos and films depicting child sex acts, LehighValleyLive.com reports.

Weintraub’s press conference on Monday included a PowerPoint presentation depicting Thomas’ business card, as well as photographs of him dating back to 1996 and previous known residences in Bucks County, Pa.

Investigators said Thomas frequently videotaped the alleged attacks and recordings were recovered from his home, although they had yet to be reviewed, CBS Philly reports.

Anyone who believes they have been victimized by Thomas is asked to call the Falls Township Police Department at (215) 302-3315.