LOS ANGELES (CBS SF) — A USC adjunct professor was detained by the Los Angeles Police Department after she allegedly told her students there was an active shooter inside a campus building, triggering a SWAT response and a shelter-in-place.

The incident took place on Monday and involved an adjunct professor in the management communication department. About five minutes into class, students said, the instructor said she heard gunshots and ordered the students to barricade the door.

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Sophomore Christopher Rawlings told the Daily Trojan that his instructor then fled the classroom, leaving the students to fend for themselves around noon on Monday.

“I, for one, just thought it was a drill and that she was acting the whole time,” Rawlings told the student newspaper. “But as time went on and I was getting messages from everyone asking if I was OK … it became more and more real to the people in the room.”

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Campus police were alerted and a SWAT team was sent to Fertitta Hall which was searched room by room. A campus wide shelter-in-place was also ordered. The all clear was given later in the afternoon.

Campus police chief John Thomas told the Daily Trojan in an email that the all clear was given after 1 p.m.

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“The faculty member has been detained by the LAPD,” Thomas said in the email.