In Letter from Jail, Matthew Taylor Coleman Admits 'Delusion in My Own Mind' Before Child Murders

Sitting in his cell at an undisclosed federal prison in California, Matthew Taylor Coleman wrote a two-page letter to a friend detailing how his thinking has changed in the 10 months since he allegedly killed his two children in Mexico with a spearfishing gun.

In the letter, handwritten on lined notebook paper, Coleman addressed some of his alleged conspiratorial thinking — including his belief that his wife, Abby, had reptile DNA that she passed down to the couple's kids, Kaleo, 2, and Roxy, 10 months. Coleman has been charged with two counts of foreign first-degree murder of United States nationals, and has pleaded not guilty.

"I was deceived," Coleman wrote in the letter, which was viewed by PEOPLE. "I was deceiving myself. I know now that the [reptile] DNA thing was a delusion in my own mind. I made myself believe something that wasn't there."

On Aug. 7, 2021, Matthew and Abby were packing for a family trip. Authorities allege that Matthew abruptly put Kaleo and Roxy 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 Matthew would eventually return home with the kids.

But he didn't return, instead allegedly driving 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, Matthew was allegedly motivated by various outlandish conspiracy theories.

"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.

Authorities allege Coleman believed in 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.

In a later affidavit, Abby allegedly told authorities she had also researched QAnon with her husband, but said he "became significantly more paranoid that people around him were involved in a conspiracy." Friends told PEOPLE earlier this year that Coleman spent hours a day on websites and message boards, reading about conspiracy theories.

PEOPLE has not been able to reach Coleman's public defender.

But now Coleman is in jail with no access to conspiracy websites. In his letter, he explains that he's processing through his beliefs.

"I'm sorting through it all now," he wrote. "There's a lot to unpack, but I have to figure out what I really believe, but I don't have access to information anymore, so I'm having to use my mind to figure things out."