Anthony James Polito, 67, also had mailed nearly two dozen suspicious letters to faculty at universities across the country and had prepared a "target list" of people at both UNLV and a North Carolina university where he once worked, police said.
Polito, facing eviction from his home in the Las Vegas suburb of Henderson, had a criminal record of computer trespass dating to 1992 in Virginia, but police said there were no advance signs of violence.
The Taurus 9mm handgun he used in the shooting was legally purchased in 2022, according to Sheriff Kevin McMahill of the Las Vegas Metropolitan Police Department. He said Polito, who police shot dead after the attacks, was believed to have acted alone.
The precise motive for the rampage remained to be determined, though officials said it appeared students were not the primary target.
All four people shot on Wednesday inside Beam Hall, the campus building that houses UNLV's business school, were faculty members.
Two of the dead were identified as professor Cha Jan "Jerry" Chang, 64, and assistant professor Patricia Navarro Velez, 39. The identity of the third slain professor was being withheld pending notification of family.
The surviving victim remained hospitalized, and his condition worsened on Thursday, McMahill said.
Detectives learned Polito had visited a post office shortly before the shooting and mailed 22 letters with no return address to university personnel across the United States, and had a list of people he was seeking on the UNLV campus as well as faculty from his former employer, East Carolina University in Greenville, North Carolina.
His LinkedIn profile described Polito as a semi-retired associate professor of business who taught at East Carolina from 2001-2017.
Authorities intercepted the letters before any were delivered and found a suspicious white powdery substance in at least one of them, McMahill said at a news briefing on Thursday.
The letters' contents remained under investigation, the sheriff told reporters, warning that anyone in higher education who received such an envelope should exercise caution and contact authorities.
He said officials were working to notify the intended recipients and had contacted nearly everyone on the separate target list to make sure all were safe.
"None of the individuals listed on the target list became a victim," he told reporters.
He said detectives also had uncovered evidence that Polito was struggling financially, including an eviction notice taped to the entrance of his apartment. He said a document that appeared to be a will was found inside.
"We know he had applied numerous times for jobs with several Nevada higher-education institutions," McMahill added, but he did not say whether UNLV was one of them.A lone shooter opened fire on the main campus of the University of Nevada, Las Vegas, on Wednesday, killing three people and wounding a fourth before the suspect was shot dead by police, authorities said at a news briefing hours afterwards.
Police declined to publicly identify the assailant, going so far as to avoid any mention of the suspect's gender, nor did they give any information about the four victims struck by gunfire - three fatally - or their connection to the university.
The surviving gunshot victim was listed in stable condition, according to Sheriff Kevin McMahill of the Las Vegas Metropolitan Police Department.
He said several other people suffered panic attacks during the pandemonium, and a number of officers were treated for minor injuries sustained during a search of the sprawling campus for any additional victims or suspects. None were found.
No mention was made of a possible motive for the violence, and police did not disclose the type of firearm used.
Vincent Perez, a professor at the school, known by its initials UNLV, told MSNBC by phone that he had heard a lot of gunfire before taking cover on campus.
"I would say just seven, eight shots, one after another, loud and very loud," he said. "As soon as we heard that, we ran back inside and we realized this is a real shooting, and there's an active shooter on campus."Official details of the incident remained sketchy.
After receiving a call reporting gunfire on campus at about 11:45 a.m. (1945 GMT), law enforcement "immediately engaged the suspect in a shootout," UNLV police chief Adam Garcia told reporters. He said the suspect was fatally shot by campus police.
"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," the sheriff added.
McMahill said the shooting began on fourth floor of Beam Hall, a building that houses the university's business school, then moved to other floors before finally ending outside where the suspect was "neutralized."
Police said the university would remain closed at least through Friday.
The UNLV campus, located less than 2 miles east of the Las Vegas Strip, has a student enrollment of some 25,000 undergraduates and 8,000 post-graduates and doctoral candidates.
The sheriff said many students he encountered appeared to have been badly shaken, recalling how people were likewise traumatized in the aftermath of a mass shooting in 2017, when a gunman opened fire from a high-rise hotel window onto a music festival below along the Las Vegas Strip.
Sixty people were killed and hundreds more were wounded in what still ranks as the deadliest mass shooting by a single gunman in US history.
Police searching Polito's home also recovered ammunition similar to the 150 rounds he was carrying.
The UNLV campus will remain closed through Friday. The UNLV website said classes had been canceled through Dec. 10.
