The Roman Catholic bishop of San Jose, Calif., has apologized to parishioners for a diocesan decision allowing a convicted child molester to volunteer at a parish festival on school grounds last month, calling it a “mistake” and “an unfortunate circumstance.”

Bishop Patrick McGrath appeared at Sunday Mass in black clerical suit and collar and told the congregation before the service began that he takes full responsibility, though he didn't say who made the ultimate decision.

"I pledge to you I will do everything in my power to make sure this doesn't happen again," he said, according to the San Jose Mercury News.

In an open letter sent on Saturday to parishioners at Saint Frances Cabrini, McGrath said the chain of events that allowed Mark Gurries to volunteer at the parish festival on Oct. 6 “is still a matter of continuing investigation on the diocesan level.”

Bur he called the decision “a mistake” and a clear violation of diocese policy.

“Our policy is clear: No one who has been found guilty of sexual abuse of a minor or vulnerable adult can be hired as an employee or allowed to volunteer in any activity that involves children, young people, or vulnerable adults,” the bishop wrote.

“I am deeply troubled and I apologize to you that this policy was not followed. The actions of parents at the festival who enlisted the services of the sheriff’s deputy are to be commended.”

Gurries, 51, was convicted two years ago of lewd and lascivious conduct on a minor under 14 years old. He served nearly a year in county jail and remains on probation, according to the Mercury News.

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The newspaper said that under California law, registered sex offenders may be allowed on school grounds if they have written permission from the school's chief administrative official. The school principal has said that no one from the school administration had given permission. However, the parish priest, the Rev. Lieu Vu, told parents at the festival that Gurries had a letter giving him permission, according to the Mercury News.

Diocesan officials have not said who wrote the letter and whether it was authorized by the bishop.

A group of angry parents recognized Gurries at the festival and argued vehemently with the parish priest until Gurries was escorted off campus by a sheriff's deputy, according to the Mercury News. Gurries was not arrested and no one was harmed.

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