Students and faculty at Yale University were put on lockdown for nearly six hours on Monday while police searched for a gunman who was supposedly on the loose on campus, but now authorities say it was likely a hoax, and they want answers.

A SWAT team and members of the ATF were present during the search, and several streets were shut down in an effort to aid authorities after someone called police saying their roommate was armed and was on his way to campus. Several calls came in after the lockdown alert went out as frightened students saw what they believed to be a gunman, but authorities say it was likely they just saw officers in plain clothes.

“Though it is starting to tilt in the direction of an innocent mistake, it started with a purposeful and malicious call,” New Haven Police Chief Dean Esserman said. “The Yale police made the right call. They went to immediate lockdown to keep everybody safe.”

Police say the initial call was made from a pay phone about a mile away from campus, but they don’t believe the caller was a student. The warning was brief and non-specific, and authorities say they will track down the person responsible, though it’s not clear what charges he may face.

Esserman says the campus is completely safe and that no one was injured during the lockdown yesterday.

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