Bishop Patrick McGrath, head of the Diocese of San Jose, said that it was a "mistake" that allowed Mark Christopher Gurries to attend and volunteer at a Saint Frances Cabrini Parish festival on Oct. 6.
"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," McGrath wrote.
"I am deeply troubled and I apologize to you that this policy was not followed," he said.
By state law, Gurries, as a registered sex offender, is only allowed on a school property around children if he can produce written permission from a school administrator, according to the Santa Clara County Sheriff's Office. Registered sex offenders who walk onto a school property without authorization when children are present are subject to arrest for a misdemeanor.
Both the Sheriff's Office and the diocese are now investigating how Guirries obtained a letter allowing him on to the grounds of St. Frances Cabrini School at 15326 Woodard Road in an unincorporated area of Santa Clara County near San Jose.
"Absent that letter, he would have been arrested then and there," Sgt. Jose Cardoza said on Thursday.
Sheriff Laurie Smith will be at Saint Frances Cabrini School on Tuesday, Nov. 27 from 2 to 6 p.m. to meet with parents and respond to their concerns, McGrath said.
The diocese also plans to hold a community awareness presentation on Megan's Law, sex offender registration and Internet safety, led by members of the Sheriff's Office.
The diocese has not received any reports of anyone being harmed at the parish festival in any way, McGrath said.