Anthony Polito, the gunman authorities said killed three people Wednesday at the University of Nevada, Las Vegas, visited a post office in Henderson and mailed 22 letters to various university personnel across the country with no return address, according to Las Vegas Sheriff Kevin McMahill.

Investigators are working with the postal inspector and federal partners to process the letters, McMahill said at a Thursday news conference. McMahill indicated they were working to contact the recipients.

At least some of the envelopes had a white powder in them, but the substance was found to be harmless, Las Vegas police said Thursday evening. Further details about the letters’ contents weren’t immediately released.

Detectives are continuing to process the envelopes and are asking “anyone in the education world” who receives a letter with no return address to “proceed with caution,” McMahill said.

The gunman, who died in a confrontation with police, was a 67-year-old career college professor whose online profile paints a picture of a man fascinated by Vegas, puzzles and conspiracy theories.

McMahill said police are still trying to understand the gunman’s motive behind the shooting, noting Polito applied and was denied “numerous times” for jobs at different Nevada higher education institutions, the sheriff said.

Authorities indicated Polito was struggling financially. When they executed a search warrant at his apartment, an eviction notice was found on the door, McMahill said, noting they found a document he described as similar to a “last will and testament.”

Polito legally purchased the weapon used in the shooting, identified as a Taurus PT92 pistol, in Las Vegas about 18 months ago, a law enforcement source told CNN. Polito brought 11 magazines to the scene and had nine loaded magazines on his person at the time of the shooting, McMahill said. Police do not know how many rounds he fired, he added.

Authorities found several computers and hard drive components at Polito’s home, along with ammunition consistent with the same cartridges found at the scene and a Taurus box matching the handgun found at the scene, he said.

The Clark County Office of the Coroner/Medical Examiner identified two of the victims as ChaJan Chang, known as “Jerry,” a 64-year-old professor from Henderson, Nevada; and Patricia Navarro Velez, a 39-year-old assistant professor from Las Vegas.

The manner of death for both is classified as homicide. The third victim has been identified and the office is working to identify their next of kin.

Three patients involved in the shooting have been released from the hospital, while one patient remains hospitalized in critical, but stable condition, according to an updated release from Sunrise Hospital and Medical Center spokesperson Marissa Mussi.

No other injuries were reported and the city’s resiliency center is providing support to people on campus affected by the shooting.

What we know about the gunman

Polito’s LinkedIn page listed him as a “semi-retired university professor” in Las Vegas.

Polito had worked for schools in Georgia and North Carolina, his now-removed LinkedIn page showed. His most recent full-time employment was as a business professor at East Carolina University in Greenville until 2017.

His personal website included syllabuses for his past courses but was largely a list of “Resources” with hundreds of links to sites related to his personal interests. While it included ordinary topics like “Travel” and “Shopping,” one section was devoted to “Powerful Organizations Bent on Global Domination!”

It included links to common conspiracy theory fodder like Freemasonry, the Trilateral Commission and “The Rothchild (sic) Family.” George Soros, a common target for antisemitic conspiracy theories, is listed as one of the “Great Minds of the Twentieth Century,” alongside Albert Einstein and others.

An ECU spokesperson told CNN Thursday Polito worked at their college of business from 2001 to 2017, holding the position of tenured associate professor when he resigned.

From October 2018 to June 2022, Polito worked as an adjunct faculty at Roseman University in Henderson, Nevada, Vice President of Communications Jason Roth told CNN. Polito was part of Roseman’s Master of Business Administration program and taught two courses, Roth said.

A University of Georgia spokesperson confirmed to CNN Polito received a PhD from the university’s business college in 2002.

His personal webpage provided dozens of links related to Las Vegas and said he had made “more than two dozen trips to Vegas over the last fifteen years,” although it was not clear when the statement was originally posted.

At least two comments previously posted at his RateMyProfessors page from his time at ECU noted his interest in Las Vegas. “He’s great, we spent over 2 months just talking about Vegas,” stated one comment from 2014. Students’ ratings were mostly positive, but also stated his teaching style was “unconventional” and “unorthodox,” with a heavy focus on personal anecdotes.

In his personal biography, last edited in September 2022, Polito claimed to be a member of the high IQ society Mensa.

As a professor, Polito had an unorthodox way of teaching and would usually start his classes with stories, frequently about Las Vegas, former student Jonathan Peralta told CNN in a telephone interview.

Peralta, a resident of Raleigh, North Carolina, took Polito’s operations class at East Carolina University in 2013 or 2014 and graduated from the university in 2015. He said Polito often talked about Vegas and described the professor as “rather chill.”

“This was surprising,” Peralta said of the UNLV shooting. “The Vegas connection is what makes it so crazy because he would talk about Vegas so much.”

Peralta said Polito “captivated and entertained students” with his stories, which were most often personal and entertaining and sometimes included life lessons. Polito’s teaching style earned him a reputation for having “easy classes,” Peralta said, though some students felt like it was too personal, and they didn’t learn much.

‘It looked like every single cop in Las Vegas was at UNLV’

Polito arrived at the university just before 11:30 a.m., and police began receiving reports at about 11:45 a.m. of a shooting at the university, prompting both on- and off-duty law enforcement to rush to the campus, the sheriff said.

When officers arrived at the scene, they entered the university’s Beam Hall business school building, where students and professors were preparing for next week’s final exams, the sheriff said.

Polito moved through multiple floors and left the building around 11:55 a.m. and confronted university police, where a gunfight ensued, he said.

Polito was struck multiple times and collapsed at the scene, where officers then arrested him, McMahill said. He was declared deceased at the scene, he said.

Officers immediately started searching the building for additional suspects and located two victims on the third floor and one victim on the fourth floor, McMahill said. The fourth victim was originally shot on the fifth floor but got himself out of the building, where officers were able to take him to an ambulance and he was taken to the hospital, he said.

Police do not know how the sequence of events played out in the shooting. McMahill said. There are no cameras in the interior of the building and authorities are working to piece together the details of how this occurred, he said.

“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 shooting prompted a campuswide shelter-in-place order as authorities rushed to stop the gunman and then methodically worked to clear the buildings, McMahill said, noting they found groups of students huddled behind many of the doors.

“We all walked out of the building, hands up,” the student said. “They evacuated us out of the student union. We walked past one of the windows, the window was shot through, glass everywhere.”

The fear and panic on campus evoked memories of the Route 91 Harvest music festival massacre, which took place just miles from UNLV on October 1, 2017, and remains the deadliest mass shooting in modern US history. Wednesday’s tragedy marks the 80th school shooting in the US so far this year, 29 of which have been on university and college campuses, according to a CNN analysis.

Sheriff McMahill said the training Las Vegas authorities have undergone since Route 91 contributed to how quickly they were able to respond and stop the shooter at UNLV.

“After 1 October and all the time and effort and energy that we’ve put in together – in training with the men and women of law enforcement, the fire service and EMS – watching how seamlessly they worked together today made me very, very proud to be their sheriff,” he said.

A student was sitting outside and eating breakfast when the shots began, the student told CNN affiliate KVVU.

“I heard three loud booms and I was like, ‘Oh, what was that?’” the student said. “Police showed up, then I ran inside.

“After two minutes, more shots. I ran into the basements, and I was there for 20,” the student said. “I was just hearing a lot of shots.”

Inside Beam Hall, a professor stopped mid-lecture after a loud noise rang out in the building, said student Brett Johnsen, who was in a second-floor classroom. But the sound didn’t initially seem like gunfire, so the professor resumed teaching.

“Then an alarm came on,” Johnsen said. “I’ve never heard an alarm like that before, it didn’t sound like a fire alarm.”

The students in the class began packing things up, relatively calmly, Johnsen said.

“When we began to walk out of the class, that’s when things got real,” he said.

The look on his professor’s face turned into panic and he urged the students to get back, lock the door and get on the ground.

“If the shooter came into our classroom, we were all just basically sitting ducks,” Johnsen said.

A few moments later, the professor opened the door to check that it was clear and told the students to run. Johnsen said he ran as fast as he could down the stairs of the building and outside as far as he could go. Everyone on campus was urging each other to flee and evacuate, he said.

“It looked like every single cop in Las Vegas was at UNLV,” Johnsen added.

The university has canceled all classes through Sunday but is still considering how the campus will operate next week, when final exams are set to begin, UNLV president Keith Whitfield wrote in a Wednesday post on the school’s website.

“Today is a tragic day for UNLV,” Whitfield wrote. “We’re all still in shock as we process the unfathomable event.”

“I’m grieving for the victims of today’s senseless shooting, and my heart breaks for the many students, faculty, staff, parents, loved ones and community members who suffered through hours of painful uncertainty while officers ensured that our campus was safe and secure again,” the university president added.

President Joe Biden expressed condolences for the families impacted by Wednesday’s Las Vegas shooting and a killing spree in Texas this week. He also called on Republicans in Congress to work with Democrats to pass a ban on assault weapons and high-capacity magazines.

“Together, we must do more to prevent more families, and more communities like Austin, San Antonio, and Las Vegas, from being ripped apart by gun violence,” Biden said.

This is a developing story and will be updated.

CNN’s Cheri Mossburg, Eric Levenson, Sarah Dewberry, Sara Smart, Steve Almasy, Gillian Roberts, DJ Judd and Cindy Von Quednow contributed to this report.

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