Last Friday, Larry McQuilliams was shot and killed by police after unleashing a campaign of violence in Austin, Texas, firing more than 100 rounds in the downtown area before making a failed attempt to burn down the Mexican Consulate. The only casualty was McQuilliams himself, who was felled by officers when he entered police headquarters, but the death toll could have been far greater: McQuilliams, who was called a “terrorist” by Austin Police Chief Art Acevedo, had several weapons, hundreds of rounds of ammunition, and a map pinpointing 34 other buildings as possible targets — including several churches.

While the impetus for McQuilliams’ onslaught remains unclear, local authorities recently announced that he may have been motivated by religion — but not the one you might think. According to the Associated Press, police officers who searched McQuilliams’ van found a copy of “Vigilantes of Christendom,” a book connected with the Phineas Priesthood, an American white supremacist movement that claims Christian inspiration and opposes interracial intercourse, racial integration, homosexuality, and abortion. Phineas priests take their name from the biblical figure Phinehas in the book of Numbers, who is described as brutally murdering an Israelite man for having sex with a foreign woman, who he also kills. Members of the Phineas Priesthood — which people “join” simply by adopting the views of the movement — are notoriously violent, and some adherents have been convicted of bank robberies, bombing abortion clinics, and planning to blow up government buildings. Although McQuilliams didn’t leave a letter explaining the reason for his attack, a handwritten note inside the book described him as a “priest in the fight against anti-God people.”

More: The Christian Terrorist Movement No One Wants to Talk About