Fifty-five men, including a former sheriff's deputy and at least one attorney, were charged with possessing child pornography following an eight-month investigation, authorities said Tuesday.

The U.S. attorney's office in Los Angeles said the suspects used peer-to-peer networks to exchange graphic images and videos, then stored the files on their computers.

All were charged with possession of child pornography. Some had been charged with additional offenses, such as production of child pornography and committing crimes while registered sex offenders.

Those facing charges include former San Luis Obispo County sheriff's Deputy Bryan Jon Goossens and attorney Thomas Merdzinski of San Bernardino, said U.S. attorney's office spokesman Thom Mrozek.

A man who identified himself as Merdzinski hung up the phone after being asked for comment by The Associated Press.

Sheriff's spokesman Rob Bryn said the department conducted an internal affairs investigation into Goossens after being contacted by the FBI about the federal probe several weeks ago.

"Our focus was on any on-duty activity, like use of department equipment, review of any past practices," Bryn said. "We don't have any pending misconduct charges against him."

Goossens was placed on administrative leave during the investigation, then gave his resignation notice, Bryn said. His last day of work was last Friday, the spokesman added.

Bryn said the department first employed Goossens in 1988 as a correctional officer. He was promoted to deputy in February 1991.

"Any time a law enforcement officer is accused of misconduct, most agencies, and certainly ours, takes it very seriously," Bryn said.