LOS ANGELES (AP/CBS13) — A Santa Barbara man was charged Wednesday with killing his 2-year-old son and 10-month-old daughter with a spear gun in Mexico because he believed they would become monsters, authorities said.

Matthew Taylor Coleman, 40, is facing a federal charge of the foreign murder of U.S. nationals, the U.S. attorney’s office said in a statement. It wasn’t immediately clear whether he had an attorney to speak for him.

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Coleman confessed to the FBI during an interview that he took his two young children to Rosarito, Mexico, where he shot a “spear fishing gun” into their chests, according to an affidavit filed by an FBI agent with the criminal complaint.

Coleman said that “he believed his children were going to grow into monsters so he had to kill them,” according to the court document.

A farm worker found the children’s bodies on Monday at a ranch near Rosarito in Baja California, authorities there have said.

Coleman and the children had checked into a Rosarito hotel on Saturday, but video footage showed them leaving before dawn on Monday, Mexican authorities said.

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The man returned alone later that morning and then left the hotel for good, authorities said.

Coleman’s wife reported to Santa Barbara police on Saturday that her husband had left with the children in the family’s van, she didn’t know where they were going, and he hadn’t answered her text messages.

Coleman’s wife said she didn’t believe the children were in any danger, that she hadn’t had any problems with Coleman, and “they did not have any sort of argument” before he left, according to the court affidavit.

An iPhone-finding application placed Coleman’s phone in Rosarito on Sunday, and on Monday it was traced to an area of Mexico near the San Ysidro Port of Entry in San Diego, according to the affidavit.

Coleman was detained at the border checkpoint, where during an interview with an FBI agent “he explained that he was enlightened by QAnon and Illuminati conspiracy theories and was receiving visions and signs revealing that his wife, A.C., possessed serpent DNA and had passed it on to his children,” according to the affidavit.

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Coleman is the founder of the Lovewater surfing school in Santa Barbara.