The gunman suspected of killing three people and critically wounding a fourth before dying in a shootout with police at the University of Nevada, Las Vegas, had unsuccessfully sought a job at the school, the Associated Press reported.

Law enforcement sources told the news agency the gunman in Wednesday's shooting was a professor who had previously worked at East Carolina University in North Carolina. The source was not named because they weren't authorized to release information from an ongoing investigation to the public.

The Las Vegas Metropolitan Police Department did not immediately respond to a request for comment.

Terror struck the UNLV campus on Wednesday when a gunman opened fire on the fourth floor of the building that houses UNLV’s Lee Business School. Students and faculty followed guidance to "Run-Hide-Fight" as the shooter moved through several floors of the building before he was killed in a shootout with two university police detectives outside the building, Las Vegas Metropolitan Police Department Sheriff Kevin McMahill said. 

‘ACTIVE SHOOTER’ AT UNIVERSITY OF NEVADA, LAS VEGAS WITH ‘MULTIPLE VICTIMS;’ SUSPECT DEAD

A police officer holds up crime scene tape at the University of Nevada, Las Vegas

A police officer walks under crime scene tape in the aftermath of a shooting at the University of Nevada, Las Vegas, Wednesday, December 6, 2023, in Las Vegas. (AP Photo/John Locher)

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.

McMahill said at a press conference that the first 911 calls were placed at 11:45 a.m. He said two police officers were treated for minor injuries from searching campus rooms and buildings.

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

The police chief said there could have been many more lives taken without the actions of the officers who initially responded.

TEXAS SUSPECT IN DAY-LONG SHOOTING SPREE THAT LEFT 6 DEAD, 3 INJURED ARRESTED, CHARGED WITH CAPITAL MURDER

Las Vegas Metropolitan Police respond to shooting at UNLV campus

A police officer works the scene of a shooting on the University of Nevada, Las Vegas campus on Wednesday, Dec. 6, 2023, in Las Vegas. (Madeline Carter/Las Vegas Review-Journal via AP)

"Importantly, there was a gathering just outside of the building where the students were playing games and eating food. . . . And if it hadn't been for the heroic actions of one of those police officers who responded, there could have been countless additional lives taken. Armed confrontation of the suspect by law enforcement stopped the suspect's further actions," McMahill said.

Police have not yet identified the victims, the attacker, nor the weapons or motive used in the shooting. Witnesses reported hearing as many as 20 shots fired during the attack, according to the AP. 

An Associated Press map shows the shooting location at UNLV

A shooter opened fire at the University of Nevada, Las Vegas on Wednesday. (AP Digital Embed)

Classes and school activities have been canceled through Sunday and the UNLV basketball game at the University of Dayton, Ohio, was canceled Wednesday because of the shootings. 

UNLV President Keith E. Whitfield released a statement following the horrific attack on Wednesday.

SUSPECTED LOS ANGELES SERIAL KILLER GOT $700K SETTLEMENT FROM SANTA MONICA BEFORE SHOOTING SPREE

University of Nevada, Las Vegas, students pray after shooting on campus

University of Nevada, Las Vegas, student Carlos Casillas, 23, second from right, prays at the Las Vegas Convention Center reunification area where he was transported after a fatal shooting at the campus in Las Vegas, Wednesday, December 6, 2023. (Wade Vandervort/Las Vegas Sun via AP)

"Today is a tragic day for UNLV. It is with the utmost sadness and grief that I am writing to you about a shooting that took place late this morning on our campus – our home. We're all still in shock as we process the unfathomable event. Members of our community lost their lives and others were injured. My heart aches for our UNLV family. I know all of us are sending our love and support to the victims, their families, and friends during this difficult time," Whitfield wrote. 

Whitfield said mental health support services and counseling are available on campus for students and staff. The school is cooperating with law enforcement as police investigate the shooting.

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"I am incredibly grateful to the countless first responders from University Police Services, the Las Vegas Metropolitan Police Department, Clark County Fire Department, and all emergency responders and medical personnel for their immediate and dedicated response," Whitfield wrote. "Their actions today were brave, heroic, and indicative of the strength and resilience of our community."

Fox News Digital's Adam Sabes and the Associated Press contributed to this report.