The Rev. Jose Magana said he decided to bring out the relic this year, on the 780th anniversary of the death of St. Anthony, because many of his parishioners have lost hope in the rough economy.
Magana said the relic is invaluable and deeply symbolic to his parish.
"It's our history, so it's irreplaceable," Magana said. "It belongs to the church, not just the church here in Long Beach, but the entire Catholic church."
The church opened at 6 a.m., and when Magana turned to the relic during the 9 a.m. Mass, it had disappeared. Magana could hear his parishioners gasp when they realized it was gone, but he continued with the service and called police immediately afterward.
Long Beach police Lt. Paul Arcala said the relic is housed in a 16-inch tall reliquary case with angel-shaped handles made of gold and silver on either side. He declined to describe it further because that might jeopardize the investigation.
The last time it was on view was eight years ago, to celebrate the 100th anniversary of the parish. In Catholicism, relics are usually part of a saint's body or clothes and revered as a physical connection to the saint.
While church members are upset that someone would steal a holy object, their faith is still strong.
"They said, `Father, he's the patron saint of lost causes, so he'll come home,"' Magana said.
Police were looking for a person who was seen at all five Masses on Sunday and was unusually curious about the relic, Arcala said. Witnesses said she got too close and had to be asked to step away. The woman was in her late 30s and was short and heavyset with wavy, shoulder-length black hair.
"I'm hoping we've got some higher sources who've got our backs here and we can get it back," Magana said. "People here are pretty upset but they're praying. They're praying to St. Anthony for the return of his own object."