A former college professor, facing financial difficulties and armed with a "target list," fatally shot three faculty members and wounded a fourth at a Las Vegas campus, according to police.

During the attack at the University of Nevada on Wednesday, the 67-year-old suspect was fatally shot by the police. Authorities suggested that being turned down for "several" jobs at different colleges might have been a motive for the shooting.

Prior to the incident, the suspect had also sent a parcel containing white powder to at least one university.

The two identified victims are professors Cha Jan Chang, 64, and Patricia Navarro-Velez, 39, while the name of the third victim will be disclosed after notifying the family, as stated by college officials. The fourth victim, a 38-year-old visiting professor, remains in critical condition in the hospital.

Police reported that all individuals on the suspect's target list have been contacted, with the exception of one person who is currently traveling internationally.

"None of the individuals on the target list became a victim," Clark County Sheriff Kevin McMahill told reporters on Thursday.

The gunman, Anthony Polito, was carrying a legally purchased .9mm pistol and 11 magazines, police said. Investigators are still trying to determine how many shots were fired.

The BBC's US partner CBS News reports that 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.

Shortly before the shooting, the suspect went to a local post office and sent 22 letters to universities throughout the country.

Sheriff McMahill said one of the envelopes mailed by Polito was found to contain an unknown white powder, which investigators have sent for testing.

Police also have searched the suspect's apartment in the nearby city of Henderson, and seized electronics.

Sheriff McMahill said when investigators arrived at the suspect's home they found an eviction notice taped to the front door.

The gunman's online presence - through his personal website, LinkedIn profile and Twitter account- provides no clear indication as to 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 afterwards 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.

One former student of Polito told WTVD-TV in North Carolina that the lecturer would obsess over online "negative feedback" from students.

"One of the things that always stood out to me that made me uncomfortable was he would try to figure out who wrote the negative feedback," Paul Whittington told the outlet. "And a lot of the negative feedback was shared with us in class."

Polito opened fire just before noon on Wednesday, and police gave the all-clear about 40 minutes after the first report of an active shooter.

Sheriff McMahill said the university police's quick response had saved lives.

Four other people were also taken to hospital for panic attacks and two police officers were treated for minor injuries.

One student told a local ABC station of the fear on campus during the shooting.

"You don't know what to do," said the student. "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".

The campus, about two miles from the world-famous Las Vegas Strip, will remain closed on 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 60 people were killed at a music festival in 2017.

So painful

Too bad