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Three people were killed and another injured after a gunman opened fire on the University of Nevada, Las Vegas, campus Wednesday afternoon.

The suspect, described as a former college professor in his 60s, was killed in a shootout with police.

He has not been named, but sources identified him as Anthony Polito, 67, to the ´óÏó´«Ã½'s US partner CBS News.

Police are expected to name the victims at a news conference on Thursday. Media reports say none were students.

Investigators at the state, local and federal levels are currently digging into what drove the Wednesday shooting, which also injured one person.

CBS News reported that Mr Polito, a former business professor who had taught in Georgia and North Carolina, had applied for a position at the UNLV but did not get the job.

Officials told the ´óÏó´«Ã½ partner network that being denied the position may have factored into his motive for the attack.

Speaking at a Wednesday press conference, Kevin McMahill, the Las Vegas Metropolitan Police Department's sheriff, said that they had "no idea on the motive" as of now and did not have details on the weapon used in the shooting.

Mr Polito's online presence - through his personal website, LinkedIn profile, and Twitter account- provides no strong indications of why he might have opened fire at UNLV's business school.

He had been a tenured associate professor at Eastern Carolina University when he resigned in 2017. He started teaching there in 2001.

He appears to have moved to Nevada soon after and referred to himself as "semi-retired" on his personal website. He wrote positively about Las Vegas, posting on his site that he had "had the pleasure of making more than two dozen trips" there over 15 years.

Police have searched an apartment believed linked to the suspect in the nearby city of Henderson, and have seized electronics as possible evidence, CBS reports.

The university first tweeted at around 11:53 local time (19:53 GMT) on Wednesday that police were responding to reports of shots fired on campus.

About 20 minutes later, the university said campus police were responding to an additional report of shots near the Student Union building.

It warned students at Beam Hall, home to the university's business school, to "evacuate to a safe area" and to "RUN-HIDE-FIGHT", which is a common active shooter protocol in the US.

The gunman moved among the floors of Beam Hall before exiting the building, according to police.

Adam Garcia, university police chief, said the suspect was then killed in a shootout with two officers.

Sheriff McMahill said the university force's response saved the lives of students who were gathered outside of Beam Hall playing games and eating food.

"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," he said.

The surviving shooting victim is in stable condition at a local hospital, the sheriff said. Four other people were also taken to hospital for panic attacks and two police officers were treated for minor injuries.

One student who was on campus told a local ABC station that it seemed like police were on campus right away.

Describing the scene to the reporter he said: "You don't know what to do. You're calling your family, texting your friends like 'I love you guys' because he [the shooter] could burst through the door at any minute."

President Joe Biden said in a statement that UNLV is the "latest college campus to be terrorized by a horrific act of gun violence" and that he and First Lady Jill Biden are "praying for the families of our fallen".

The campus, about two miles from the world-famous Las Vegas Strip, will remain closed through Friday.

There have been more than 630 mass shootings in the US this year. Las Vegas is also the site of the deadliest mass shooting in modern US history, where more than 50 people were killed at a music festival in 2017.