LAS VEGAS (AP) — 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.

Another law enforcement official identified the suspect as Anthony Polito, 67. Investigators searched an apartment in Henderson, Nevada, late Wednesday as part of the investigation and retrieved several electronic devices, including Polito's cellphone, the official said. The official was not authorized to discuss details of the investigation and spoke to AP on condition of anonymity.

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.

Lessons learned from that shooting — the deadliest in modern U.S. history — helped authorities to work "seamlessly" in reacting to the UNLV attack, Las Vegas Metropolitan Police Department Sheriff Kevin McMahill said at a news conference.

The gunman opened fire about 11:45 a.m. on the fourth floor of the building that houses UNLV's Lee Business School and then went to several other floors before he was killed in a shootout with two university police detectives outside the building, UNLV Police Chief Adam Garcia said.

Authorities gave the all-clear about 40 minutes after the first report of an active shooter.