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Peter Tersigni, who lives in Michigan, said he had known Mr. Sanford since preschool and called him his best friend. A four-year stint in the Marine Corps, including time in Iraq, changed his friend from the former class clown into a more serious person, Mr. Tersigni said.

But his time living in Utah and heavy use of methamphetamine appeared to change him more. There, he fell in love with a woman who was a member of the Church of Jesus Christ of Latter-day Saints, and the relationship ended painfully, his friend said.

“Mentally he was in rough shape” when he returned to Michigan, Mr. Tersigni said.

From then on, Mr. Sanford had a problem with members of the Church of Jesus Christ of Latter-day Saints and wasn’t shy about sharing it, Mr. Tersigni and his twin brother, Francis Tersigni, recounted in separate interviews on Monday.

“He got this whole fascination with Mormons, and they are the Antichrist, and they are going to take over the world,” Francis Tersigni said. It even came up at Peter Tersigni’s wedding, his brother recalled. “All he could talk about was Mormons,” he said. “I was like, dude, nobody wants to hear about this stuff.”

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As recently as last week, Kris Johns, a candidate for the City Council in Burton, Mich., knocked on Mr. Sanford’s door while canvassing and, within a few minutes, found himself listening to a diatribe about Mr. Sanford’s ex-girlfriend, the church and its demands that he remove his tattoos to become a member.

Mr. Johns remembers Mr. Sanford saying repeatedly, “Mormons are the Antichrist.” He described Mr. Sanford as calm, not making any specific threats, but “under the surface, extremely angry.”