Terrified students and professors cowered in classrooms and dorms as a gunman roamed the floors of a University of Nevada, Las Vegas building, killing three people and critically wounding a fourth before dying in a shootout with police.

The gunman in Wednesday’s shooting was a professor who had unsuccessfully sought a job at the school, a law enforcement official with direct knowledge of the investigation told The Associated Press. He previously worked at East Carolina University in North Carolina, said the official, who spoke on the condition of anonymity because they weren’t authorized to release the information publicly.

The attack was the worst shooting in the city since October 2017, when a gunman killed 60 people and wounded more than 400 after opening fire from the window of a room at Mandalay Bay casino on the world-famous Las Vegas Strip only a couple miles from the UNLV campus.