SAN JOSE  (AP) — A Catholic bishop in San Jose has apologized to worshippers for allowing a registered sex offender to volunteer at a school festival last month.

Diocese of San Jose Bishop Patrick McGrath told the St. Frances Cabrini congregation during Sunday mass that he takes full responsibility and promised to make sure it never happens again, according to the San Jose Mercury News.

McGrath said it was "a failure at the diocese level" that gave a permission letter to a convicted child molester Mark Christopher Gurries to volunteer at the parish festival. The bishop didn't explain how or why a letter was written and signed by someone at the dioceses.

"How this happened is still a matter of continuing investigation on the diocesan level," the bishop wrote in a letter in the parish bulletin.

Someone at the elementary school festival recognized Gurries, 51, and reported it to a security officer. The convicted molester was escorted off campus.

Gurries, who is married to a former teacher at St. Frances Cabrini, is on probation for molesting an underage relative after serving nearly a year in county jail. The conditions of his probation state that he cannot be near children.

John Borrelli, a parent at the church, said the diocese must publicly answer questions about the letter.

"They need to come forth and tell the parents what happened and why and that it's never going to happen again," Borrelli said. "The parents that believe in the school, we all deserve this."