Authorities are searching for an ancient relic -- believed to be part of Christ's Crucifixion cross -- that was stolen from a San Francisco church.

Thieves broke into St. Dominic's Catholic Church on Thursday and popped the lock on the glass case that housed the artifact before fleeing without a trace, ABC affiliate KGO reported. 

Church leaders and parishioners expressed their grief over the church's most treasured possession at Mass on Sunday.

"The true cross is a relic that goes back 2,000 years to the very cross of Christ himself. For it to be stolen in this kind of very deliberate way is certainly both upsetting and very saddening," the church's pastor, Father Michael Hurley, told parishioners, according to the station.

The church reportedly has no security cameras -- and police say they have few clues to lead them to the perpetrators. 

Hurley said he's hoping the thief will have a change of heart and return the relic, the station reported.

"We're hoping that the thief will have a change of heart and perhaps we can discover it again and restore this important relic to our church," Hurley said. 

The church placed a sign on the display case asking that the thief return the relic, with no questions asked.

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