Police Investigate Internet History of Matthew Coleman, Accused of Killing Kids Over QAnon Theories

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

Matthew Taylor Coleman. Photo: Instagram

Months after he was arrested for allegedly killing his two children with a spearfishing gun in Mexico, Matthew Taylor Coleman remains behind bars without bond as he awaits trial — and now the FBI is looking into his browser history and messages, PEOPLE has learned.

In a joint motion filed last week by the United States Attorney and the Federal Public Defenders, both sides asked that the case be continued until next May so that they could continue to gather relevant evidence in the case.

One of the most daunting tasks is searching electronics owned by Coleman — and both sides agreed that they should immediately have access to the full scope of data on the devices.

"A computer, two phones, and an iPad are being searched pursuant to warrants," the motion says. "Instead of waiting until agents have completed the searches and providing only data seized as responsive to the warrants, a mirror image of the computer's entire drive and the full Cellebrite downloads for the phones and iPad will be provided to the defense by Nov. 5, 2021."

"By that date, the United States also will provide additional discovery consisting generally of cell site data, Mexican law enforcement reports, photographs and recordings of or from the area of the murders, jail recordings, and videos from the Port of Entry," the motion continues.

A federal law enforcement source confirms to PEOPLE that FBI agents are focusing on his web browsing history, text and email messages, and postings on message boards and groups that discuss QAnon conspiracy theories.

"Agents are seeing what he read," says the law enforcement source, "but we're more interested in what he wrote about his beliefs and whether they had any influence over his actions in August."

Matthew Coleman, Abby Coleman, Kaleo Coleman, Roxy Coleman.

Want to keep up with the latest crime coverage? Sign up for PEOPLE's free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.

A lifelong friend of Colemans previously told PEOPLE that Coleman spent an increasing amount of time online looking at conspiracy theory websites and message boards.

"It was obvious that he was spending a lot of brainpower on it," the friend, who has known Coleman since they were children, told PEOPLE last month. "He was constantly checking those sites on his phone. He spent hours each day just glued to his phone looking at that stuff."

Police say Coleman 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.

Kaleo and Roxy Coleman. Matthew Taylor Coleman/instagram

According to an FBI criminal complaint obtained by PEOPLE, 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.

In the criminal 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 was indicted on murder charges in September. If convicted, he is eligible for the death penalty. Coleman is now being held in protective custody. He has not yet entered a plea, and the public defender's office has not returned PEOPLE's calls for comment.