Authorities started investigating Mraz after they got a call from the Diocese of Allentown, Lehigh County District Attorney James Martin said Tuesday at a news conference.
The Diocese said in a statement that Mraz has been removed from public ministry and "cannot present himself as a priest."
"These kinds of cases are frequently found among people who … are held in high regard – business people, successful people in all walks of life," Martin said. "It's always disappointing to me … that people have a proclivity to do children harm."
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A parishioner contacted the diocese in late July after Mraz asked him to help upgrade one of his computers. As he was working on the pastor's computer, he found multiple photos of naked men in the recycle bin, Martin said.
Still, the parishioner agreed to upgrade a second computer for Mraz, at which time he found "a folder that implied obscene images of boys," Martin said.
Court records show the folder was named "small boy nudes," according to The Morning Call.
Authorities searched the Church of St. Ann's rectory, where Mraz was living at the time, and seized multiple electronic devices. Martin said pornographic images of children were found on the devices, although he declined to elaborate on how many were recovered.
"(We have) no evidence to show he physically had contact (with any victims)," Martin said. "(The) videos and pornographic images were made by someone and put out on the internet. … (This) is a pornography case at this point, and I hope it will continue to be."
Mraz has been away from his post for the last month with what officials said were "medical issues," The Morning Call reported.
He was arraigned Tuesday morning and released on a $50,000 unsecured bond, according to the newspaper.
Mraz was ordained in 1975 and formerly worked as a professor at a pair of Catholic high schools. He previously held the titles of vice principal and director of spiritual activities at Marian High School in Tamaqua, chaplain at the Neman Center at Lehigh University, assistant superintendent at the Diocesan Office of Education and pastor of the former St. Bertha Parish in Tuscarora.
He has been with the Church of St. Ann since 2008.