A California father took his two young children to Mexico and killed them with a spearfishing gun after he claimed he had been "enlightened by QAnon and Illuminati conspiracy theories," federal authorities say.

According to a criminal complaint filed in federal court in California, Matthew Taylor Coleman reportedly told investigators he had been "receiving visions and signs revealing that his wife possessed serpent DNA and had passed it onto his children" and that by killing them he was "saving the world from monsters."

QAnon is a conspiracy popular among some on the far right that claims Democratic politicians operate a cabal that kidnaps and tortures children, using their blood in satanic rituals.

It wasn't the first time authorities responded to a crime based on a conspiracy theory that originated on the internet.

In 2016, Edgar Maddison Welch entered a Washington, D.C., pizzeria and fired a rifle into a door, claiming he was investigating the debunked "Pizzagate" rumor. That conspiracy theory claimed that the Comet Ping Pong restaurant was the hub of a satanic child sex abuse ring associated with top Democratic politicians.

Welch was later sentenced to four years in prison.

How authorities tracked down Matthew Taylor Coleman

Coleman, 40, was first reported missing by his wife — identified in the complaint as A.C. — on Saturday. She was unable to reach him by phone after he left in the family's van with their two children, a 2-year-old boy and a 10-month-old girl.

The next day, at the suggestion of police, A.C. used the Find My iPhone application to track Coleman's last known location to an "open-air shopping center" in Rosarito in the Mexican state of Baja California.

When Coleman arrived Monday at the U.S.-Mexico border crossing in San Ysidro without his children, law enforcement officers took him into custody. Earlier that morning, Mexican authorities had discovered the bodies of two children with puncture wounds in their chests.

Coleman apparently told investigators he knew that killing his children was wrong but said it was the "only course of action that would save the world."

Mexican officials also recovered the weapon, bloody clothes and a baby's blanket, authorities said.

Coleman has been charged with the foreign murder of U.S. nationals.

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