A man who allegedly threatened the University of California, Los Angeles, also detailed potential violence against the University of Colorado, Boulder, in an 800-page manifesto, authorities said Tuesday.

The man — identified as Matthew Christopher Harris, 31 — was taken into custody Tuesday morning and is being held in Colorado on state charges after a standoff with police in Boulder. Federal charges may be pursued.

Colorado authorities “have taken into custody the individual who made threats agains some of our UCLA community yesterday,” the statement said.

UCLA tweeted overnight that in-person classes were canceled Tuesday after a “concerning email and posting” were sent to members of the university community.

“The threats made yesterday were frightening for many of us and caused our community to feel vulnerable at an already challenging time,” said a statement signed by Assistant Vice Chancellors Suzanne L. Seplow and Michael Deluca.

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UCLA took the step of switching to remote learning a day after students returned to in-person instruction and said the move was made out of an abundance of caution.

“UCLA Police Department is aware of a concerning email and posting sent to some members of the UCLA community today and actively engaged with out-of-state law enforcement and federal agencies,” the university said in a series of overnight social media posts.

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Michel Moore, chief of the Los Angeles Police Department, said earlier Tuesday that the individual who made the threats was believed to be in Colorado. Law enforcement and UCLA have not yet named the person.

“At this point we believe the campus is safe,” Moore said during a meeting of the Board of Police Commissioners.

The FBI’s Los Angeles field office is working with UCLA “to assess the situation,” FBI spokesperson Laura Eimiller told The Associated Press.

A spokesperson for the FBI’s Denver field office did not immediately respond to an email request for comment.

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The Los Angeles Times reported that it obtained emails that were sent to students and faculty showing that authorities are investigating a former UCLA lecturer who allegedly sent a video referencing a mass shooting and an 800-page manifesto with threats against individuals in the philosophy department.

UCLA’s postings did not confirm the details of the Times’ report but said: “Out-of-state law enforcement has confirmed the person who made threats to UCLA is under observation & not in CA. Classes will remain remote today.”

Bill Kisliuk, the university’s director of media relations, did not address a series of detailed questions emailed to him by the AP but said he would reach out “when we have more.” It was not clear when that might be.

The university on social media posted telephone numbers for students, faculty and staff seeking counseling.

Considered one of the top public universities in the country, UCLA is located in the affluent Westwood neighborhood of Los Angeles. The university has more than 31,000 undergraduate students and 14,000 graduate students.

UCLA’s threats appear to be unrelated to bomb threats made Monday — one day before the start of Black History Month — to at least a half-dozen historically Black universities in five states and the District of Columbia, Eimiller said.

The UCLA campus was rocked by a shooting in 2016 when a former student killed his estranged wife in a Minneapolis suburb and traveled to UCLA, where he fatally shot an engineering professor who had been his mentor and then killed himself.