Matthew Coleman, The Dad Who Allegedly Killed Kids Over QAnon Theories, 'Deteriorated Rapidly': Friend

In the months before Matthew Coleman was arrested for allegedly killing his children, the father of two spent an increasing amount of time online looking at conspiracy theory websites and message boards — but even those closest to Coleman had no inkling that his actions could turn violent.

"He started believing crazy things that he saw on the internet," one of Coleman's childhood friends, who was in touch with him a week before the killings, tells PEOPLE. "But nothing seemed violent. He just seemed to be buying a lot of stuff that didn't make a lot of sense."

"It started off slowly, but near the end, he deteriorated rapidly," the friend said. "But he never once said anything to make anyone think that he'd kill his own kids. That's another level."

On Aug. 7, Coleman and his wife, Abby, 35, were packing for a family trip. Authorities allege that Coleman abruptly put his two kids — Kaleo, 2, and Roxy, 10 months — into his van and drove away from their Santa Barbara, Calif., home.

Abby called police out of concern. 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 thought Coleman would eventually return home with the kids.

But police say Coleman didn't return and instead drove the children into Mexico. Two days later, authorities allege, he took the kids to a ranch, where 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.

According to an FBI criminal complaint obtained by PEOPLE last August, Coleman allegedly told police he was motivated by the QAnon conspiracy theory, which falsely claims President Donald Trump has secretly been battling a cabal of Satan-worshipping pedophiles at the highest levels of political power and influence.

But a newly released affidavit further details Coleman's conspiratorial beliefs. He allegedly told agents that while he was in Mexico, he had laid in bed "seeing all the pieces being decoded like The Matrix, and that he was Neo."

"He said visions and signs revealed that his wife, A.C. [Abby Coleman], possessed serpent DNA (M. COLEMAN mentioned that he was not sure if his wife was a shapeshifter) and had passed it onto his children and that all things were pointing to the idea that his children have corrupted DNA that will spread if something is not done about it," according to the affidavit.

The latest affidavit has confused those who knew him.

"That sounds crazy," Coleman's childhood friend said. "He never said anything about serpent DNA to me, and I assume he never said anything about it to Abby. We knew he was in turmoil, figuring things out, but no one — especially not Abby — thought he'd get violent."

Coleman's friend said that his wife and loved ones truly believed the children's well-being was top priority for Coleman.

"I'm going to make one thing perfectly clear," the friend said. "Abby loved those kids more than anything, and we all believed that Matthew did too. If anyone had even one thought that he was violent or dangerous, we would've done everything to stop it. This came out of left field for all of us, and we have to live with that every day for the rest of our lives."