Dallas City News

Federal investigators have uncovered thousands of links from the online phone history of the gunman who tried to assassinate former President Donald Trump, including searches involving a teenage mass shooter in Michigan, according to two law enforcement sources.

The sources said Friday that Thomas Matthew Crooks‘ phone had searches on it regarding the Oxford High School shooting and gunman, who was 15 when he fatally shot four students and wounded several others in suburban Detroit in 2021. He was sentenced to life in prison.

The attack also led prosecutors to charge his mother and father, Jennifer and James Crumbley, with involuntary manslaughter. This year, they became the first parents in the U.S. to be held partially responsible for their child’s school shooting, and were sentenced in April to 10 to 15 years in prison.

That same month, Crooks, 20, performed internet searches about depressive disorder, the law enforcement sources said. In May, he did research on explosive materials and chemical compounds for such a device. At some point, he also looked up an article about improvised explosive devices and the Department of Homeland Security.

There were more than 14,000 links and links to images found on his phone, the sources added.

Among the images investigators said they found on his phone was of Saturday’s rally in Butler, Pennsylvania, shortly before the shooting began after Trump took the stage at about 6 p.m.

The former president survived the attack, which left a former fire chief dead and two other attendees injured. The gunman, who used an AR-15-style rifle, was killed amid the chaos at the Butler Farm Show, and the aftermath of the shooting has placed scrutiny on law enforcement’s failure to secure the scene and other breakdowns in planning.

The gunman’s motivation remains elusive, with investigators saying they believe he acted alone and there was no obvious political ideologies that he could be linked to. Public records show that he was a registered Republican but in 2021 donated $15 to a progressive voting effort. Investigators also found the gunman had made searches this month specific to Trump, a rally and the Democratic National Committee, according to a senior law enforcement official.

Some former classmates at Bethel High School in suburban Pittsburgh, where the gunman resided with his parents, have had recollections of him being a quiet student with a small friend group.

An uncle, Mark Crooks, told NBC News on Monday that he hadn’t seen his nephew in years and didn’t keep in close contact with that side of the family because they were private. He also said he didn’t know about his nephew’s political leanings or what would have motivated him to try to assassinate Trump.

Authorities said they confiscated more than a dozen guns from the family’s Bethel Park home and that they are cooperating with the investigation.

In May, around the time investigators say the gunman was searching online about explosives, he had earned an associate’s degree in engineering science from the Community College of Allegheny County. One friend said he talked about becoming a mechanical engineer.

This story first appeared on NBCNews.com. More from NBC News: