A Pennsylvania handyman accused of serial child rape kept a "perverse shrine" in his trailer home — 1,000 pairs of used girl's underwear — and documented his crimes in hundreds of disturbing, graphic images and writings, authorities said.

Investigators said William Charles Thomas' crimes were discovered because he wrote about sex assaults on a piece of plywood that he used in a renovation project.

Thomas, 58, of Morrisville, was arraigned Tuesday on 51 charges, including five counts of child rape, and was jailed on $750,000 bail. Authorities urged other victims to come forward, saying Thomas wrote about molesting children as young as 3 and as far back as the 1970s.

"To be blunt about it, this is a real-life boogeyman," Bucks County District Attorney Matthew Weintraub said at a news conference.

Thomas could not be reached for comment in jail. Court documents do not list an attorney who could comment on his behalf.

Police in the Philadelphia suburbs said they began the investigation when the owner of a trailer Thomas had just renovated found the plywood on which Thomas had written about sexually assaulting two young girls, authorities said.

Police searched Thomas's trailer and found — in addition to the underwear, drawings and his written accounts — more than 1,000 images of child pornography, including Polaroid photos with the names of three of the victims listed in court documents "as well as names of children who have yet to be identified," a police affidavit said.

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"This was a perverse shrine to his criminal conquests. And we are merely scratching the surface of those conquests today," Weintraub said.

Police also searched a shed on another property once owned by Thomas and found more sexually explicit accounts scrawled on the walls, court documents said.

Thomas told police he had been sexually attracted to children since adolescence, the affidavit said. He said he would occasionally steal girls' underwear while working as a contractor in customers' houses. Some of the underwear was found hanging over his bed, court documents said.

Falls Township Police Lt. Henry Ward called the scene inside Thomas's trailer horrific.

"Try to come up with your worst scenario and times that by 10. And it'll get close to what we saw," he said.

Court documents cite abuse dating at least to the 1990s.