LOS ANGELES (AP) — A former lecturer at the University of California, Los Angeles who was arrested Tuesday after police say he emailed an 800-page document and posted videos threatening violence against the school, had previously sent messages saying he would “hunt” and kill a professor, court documents show.

Matthew Harris, 31, was taken into custody in Colorado following a standoff at his Boulder apartment complex that ended peacefully.

The investigations in California and Colorado began this week after Harris, who had lectured in the UCLA philosophy department, sent the email to some of his former students. UCLA officials canceled classes on campus Tuesday and the university’s police department tracked Harris to Boulder and reached out to law enforcement there.

University officials did not describe the email but Los Angeles Police Department Chief Michel Moore said Harris was “potentially planning for a mass violence or shooting event at UCLA.” The university has more than 31,000 undergraduate students and 14,000 graduate students.

In Boulder, Police Chief Maris Herold said officials reviewed the manifesto and “we identified thousands of references to violence, stating things such as killing, death, murder, shootings, bombs, schoolyard massacre in Boulder and phrases like ‘burn and attack Boulder outside of the university.’”

Herold said police had contact with Harris in October, though no criminal charges were filed, and authorities are reviewing their reports from that encounter.

Authorities said he attempted to buy a handgun in November but his purchase was denied. Officials believe the transaction did not go through because of a California-based protection order that said he could not purchase or possess a firearm.

Harris was placed on leave from UCLA last year and a female University of California, Irvine philosophy professor was granted a restraining order against him after he sent emails to his mother threatening to “hunt” the professor and “put bullets in her skull.” Harris’ mother alerted the woman.

Harris’ mother and the woman could not be reached for comment.

Harris was being held in Colorado on state charges and federal charges may be pursued. It wasn’t immediately known if Harris had a lawyer who could speak on his behalf.

The police search for Harris began after he sent his former students an email early Sunday that was full of slurs against Jewish and East Asian people, according to the Los Angeles Times. The email included links to what police termed a manifesto and videos, the Times reported, including one titled “UCLA PHILOSOPHY (MASS SHOOTING).”

Harris makes racist comments in several of the videos and cryptically names specific locations on the UCLA campus, noting that they’ve been added to his “list,” according to the Times.

The UCLA video included footage from the 2017 mass shooting at a Las Vegas music festival, the newspaper reported, as well as clips from “Zero Day” – a 2003 film that was loosely based on the mass shooting at Colorado’s Columbine High School.

Harris, who didn’t appear to have any criminal record, began working at UCLA in the spring of 2019 as a postdoctoral fellow, according to a newsletter from the university’s philosophy department. His focus was on “philosophy of race, personal identity, and related issues in philosophy of mind.”

On bruinwalk.com, a website where UCLA students can post anonymous reviews of professors and other staff members, Harris got low ratings. In one review, a student wrote that Harris is “extremely unprofessional.”

“I have no idea how this guy is still teaching,” another student wrote.

Harris came to UCLA after completing his dissertation, “Continents in Cognition,” at Duke University in 2019. Duke is where he first met the woman who was the subject of the restraining order. They had “minimal contact” but he reached out to her to discuss career advice in September 2020 because he had recently moved to Los Angeles, according to the court documents.

The woman initially was happy to meet with Harris, but “their initial interaction left her feeling very uncomfortable and concerned about his behavior,” the court documents said.

Harris allegedly “began an aggressive campaign” of text messages and emails to the woman, leading her to fear for her safety. She told him to stop contacting her in March 2021.

Separately, UCLA that month placed him on investigatory leave for “predatory behavior” when the school had found he sent pornographic and violent content to students, court documents state.

In April, the professor was contacted by Harris’ mother, who told her that four months earlier her son had sent her emails saying he wanted to move closer to the Irvine campus where the professor worked so he could kill her, court documents show. UC Irvine is about 50 miles south of UCLA.

“I wouldn’t be able to live with myself if I did nothing and someone got hurt,” Harris’ mother wrote to the woman. His mother had not seen her son in five years and believed he was in need of psychiatric help, court documents show.

The University of California regents sought a workplace violence restraining order last May, the day after UCLA officials learned Harris had been released from a mental health facility and was back in Los Angeles. A temporary restraining order was granted immediately, and a longer protective order – in place until 2024 — was approved less than a month later.

The court documents say that UCLA’s police department and its Behavioral Intervention Team were aware of the threats against the professor and reached out to the FBI.

The UCLA director of media relations did not immediately return a request for comment Tuesday about the restraining order. The FBI did not immediately comment.