UCLA has reverted to remote learning after students and faculty received a threatening email and social media post from a former instructor, CBS Los Angeles reports.

At about 11:57 p.m. on Monday night, the school announced that all classes would return to remote learning Tuesday “out of an abundance of caution.”

UCLA had just gone back to in-person learning Monday after holding classes remotely due to the recent COVID-19 surge.

The “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 statement. “We will keep the community informed as we learn more.”

A campus safety alert says authorities don’t know whether the email sender is in California. “UCLA is actively working with out-of-state and federal agencies on threats sent to some members of our community,” the school tweeted.

According to the student newspaper, the Daily Bruin, the email and posting were from a former philosophy postdoctoral researcher and lecturer.

The newspaper cites Philosophy Department emails as saying the emailer sent “several communications” to department faculty and students that included “a link to his YouTube video titled ‘UCLA Philosophy (Mass Shooting)’ and an 800-page manifesto outlining threats.”

The video has been taken down by YouTube.