Students who say they received the email tell Eyewitness News they're still in shock.
"When I first got the email from him, I was beyond terrified," said UCLA student Joey Sigala. "I had just finished class, and I was shocked to my core."
Matthew Harris, 31, was taken into custody Tuesday in Colorado following a standoff at his Boulder apartment complex that ended peacefully. Colorado prosecutors said late Tuesday that federal charges were pending against Harris and that he was transferred to federal custody. It wasn't immediately known if Harris had a lawyer who could speak on his behalf.
READ MORE | Suspect in shooting threats against UCLA now in custody, authorities say
Months before the threats against UCLA, Harris was the subject of a restraining order after sending threatening messages saying he would "hunt" and kill a professor, court documents show.
UCLA officials canceled in-person classes Tuesday after police said Harris, who had lectured in the UCLA philosophy department, sent the email early Sunday to some of his former students.
"What was really, really scary to me, personally were the threats to our class, saying that it was our fault that he got fired from the university in that retaliation," UCLA student Lina Campillo told ABC7 on Tuesday. "He even called out some of my former classmates by name in the manifesto."
The university's police department tracked Harris to Colorado and reached out to law enforcement in Boulder on Monday. 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."
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 philosophy professor at the University of California, Irvine 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, 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 "began an aggressive campaign" of text messages and emails to the woman, leading her to fear for her safety, according to court documents. 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.
"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 document 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 has not answered The Associated Press' questions about the restraining order or the timeline of events leading up to the threats, as well as what occurred this week. The FBI has declined to comment.
The Associated Press contributed to this report.