Jul. 3—A Ligonier Township man was arrested late last week and charged with 25 counts of child pornography possession and five counts of sharing child pornography, after a police investigation led to the seizure of computers at his home, according to court records.

Members of the state attorney general's Child Predator Section, Internet Crimes Against Children and Regional Computer Crimes task forces began an investigation into peer-to-peer file-sharing networks, collecting information about people using the BitTorrent client program to download digital pornography files known to law enforcement.

BitTorrent works in part by assembling one file from many small pieces across a network. A user will search for a particular file, and the BitTorrent client downloads it by pulling parts from other computers on the network that have also accessed it.

"Law enforcement can then attempt to download/copy any of the files believed or otherwise known as child pornography directly from the host computer," Special Agent Duane Tabak wrote in an affidavit of probable cause. "This is known as a single-source download (as opposed to obtaining the files from multiple peers on the network)."

An investigation initiated in March turned up one torrent file known by its unique identifying markers. It was tracked back to a host computer registered to an address on the 1300 block of Darlington Road.

A search warrant executed at the address on June 29 gave police access to a computer, two hard drives and an electronic storage device determined to belong to Mathew L. Hoffer, 57, of Ligonier Township, according to court records.

Hoffer told task force officers he "knew why the police were at his residence," Tabak wrote in the affidavit. An agent with the task force found the BitTorrent program running on Hoffer's computer, police said.

More than 25 files of apparent child pornography were found during an initial search of Hoffer's computer, including both photos and videos.

Hoffer was charged with five counts of disseminating child pornography, 25 counts of possession of child pornography and criminal use of a computer.

He was arrested and arraigned June 29 and taken to Westmoreland County Prison. An attorney for Hoffer was not listed in court records.

A July 7 preliminary hearing is set for District Judge Denise Thiel's Ligonier court.

Patrick Varine is a Tribune-Review staff writer. You can contact Patrick by email at pvarine@triblive.com or via Twitter .