Police fear they are just "scratching the surface" of sex crimes committed by a suspected child rapist, after more than 1,000 pairs of soiled little girls' underwear were allegedly found in his Pennsylvania trailer.

Detectives in Bucks County said they faced "horrific" scenes after discovering the "trophies" at the home of 57-year-old William Charles Thomas.

His trailer, in the Midway Village Trailer Park in Morrisville, where he worked as a handyman, was raided after Thomas was charged with the sexual assault of as many as five children.

"The human race hasn't come up with words to describe what we saw in that trailer... try to come up with your worst scenario and times that by 10, and you'll get close to what we saw. It was horrific," said Lt. Henry Ward of the Falls Township Police Department.

On Monday (6 February), investigators released photos of Thomas spanning more than 20 years in the hopes additional victims might be able to identify him.

Currently, his youngest alleged victim is aged just two, with the rest 10-years-old or under.

Thomas's arrest came after a tip-off back in November 2016 from the owner of the trailer park, who wished to remain anonymous.

A trailer where Thomas had allegedly been working was found to contain a piece of plywood with intimate, hand-written details about the sexual assault of a three-year-old child and another aged six, police said.

Bucks County District Attorney Matt Weintraub said a subsequent search of Thomas's trailer revealed more than 1,000 images of child porn and more than 1,000 pairs of soiled little girls' underwear.

"These pairs of underwear were displayed almost throughout his mobile trailer home," said District Attorney Matt Weintraub.

"This was a perverse shrine to his criminal conquests, and we are merely scratching the surface of those conquests today. To be blunt about it, this is a real-life boogeyman. This is your parents' worst nightmare."

He added: "I pray that there aren't any more [victims], but I expect that there will be."

Also discovered in the search of Thomas's trailer were "vulgar and graphic drawings" chronicling child sex abuse going back some 40 years, police said.

Thomas, who grew up in the area before moving to the trailer park 10 years ago, is scheduled to be arraigned Tuesday morning on 51 charges, including multiple counts of child rape, involuntary deviate sexual intercourse with a child, aggravated indecent assault on a child, and other felonies and misdemeanors.

He was already in the Bucks County Correctional Facility after being charged last Friday with possession and dissemination of child pornography.

If convicted, police say he could face life in jail.

Anyone with information about other victims or Thomas' activities is urged to contact Falls Township Detective Sgt. Christopher Clark at 215-302-3315 or clarkpd@fallstwp.com , or to contact Bucks County Detective Lt. Robert Gorman at 215-340-8141 or rmgorman@buckscounty.org .