Matthew Taylor Coleman, 40, is charged with killing his 2-year-old son and 10-month-old daughter in Mexico on Aug. 9

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It was a crime that seemingly had no warning.

On Aug. 7, Matthew Taylor Coleman and his family were packing for a camping trip when, authorities allege, he abruptly put his two kids into his van and drove away from their Santa Barbara home, leaving his wife, Abby, wondering what happened.

Concerned, Abby, 35, called police. According to the FBI's report, she told authorities that she and her husband had not been arguing and that there was no marital strife. She told cops that she did not believe that the children were in any danger, and that she believed Coleman would eventually return home with the kids — Kaleo, 2, and Roxy, 10 months.

But she was wrong.

Police say Coleman, a 40-year-old surfing instructor, drove the children into Mexico. Two days later, authorities allege, he took the kids to a ranch, were he killed them with a spearfishing gun and returned to his hotel a few hours later. He was arrested when he attempted to cross the border back into the United States.

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Now, Abby is left wondering what happened — and how her husband could've acted out so violently.

"Abby is devastated," a family friend tells PEOPLE in its latest issue, on stands this week. "She is confused, stunned and just destroyed inside. She never had any idea he thought all these things. She thinks he just snapped. Something must have happened in his brain."

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According to charging documents, Coleman allegedly told police he was motivated by the QAnon conspiracy theory, which holds the false belief that former president Donald Trump has secretly been battling a cabal of Satan-worshipping pedophiles at the highest levels of political power and influence.

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Matthew Taylor Coleman
Credit: Matthew Taylor Coleman/instagram

PEOPLE obtained a criminal complaint that was filed in the U.S. District Court last Wednesday. In the 10-page complaint, FBI special agent Jennifer Bannon wrote that Coleman claimed to be "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."

"M. Coleman stated that he believed his children were going to grow into monsters so he had to kill them," Bannon wrote.

Coleman is now being held in protective custody in an undisclosed federal prison. He has not yet entered a plea, and the public defender's office has not returned PEOPLE's calls for comment.

While the case progresses, people close to him — including his wife — want to know what happened.

"She hopes to be able to ask him for answers face to face someday," says the friend, "but for now, she's just grieving. We all are. It's an absolute nightmare."