PITTSBURGH — A Butler County man arrested last week on charges of having child pornography allegedly admitted he had sex with three boys, authorities said.

U.S. Magistrate Judge Cynthia Eddy at a detention hearing Tuesday ordered Mark Beres, 53, of Slippery Rock held without bail pending a grand jury indictment in the case.

Federal prosecutors have already charged Beres with possession of child pornography. Those charges followed an April 23 search of his Center Street home and computer, according to court documents.

The search turned up about 500,000 images and some 550 videos of naked children, some engaged in sex acts.

At the time of Beres’ arrest, according to the U.S. Attorney’s office, he had been working as an optometrist at the Sears store in New Castle.

Beres became a target for investigation after authorities traced records of $2,716 in orders for child pornography that were shipped to his home from the New York offices of the so-called “International Co.”

Operators of that company, too, have been charged with child exploitation as well as production and distribution of child pornography.

Meanwhile, in a written statement to investigators, Beres admitted that he had “sexual contact with three boys, ages 3, 7 and 13, about 30 times,” the criminal complaint said.

That admission, authorities said, prompted concern that there could be other victims of the defendant.

Anyone with information about Beres or about the case is asked to call the U.S. Postal Inspection Service at 412-490-6513.