One day after a mass shooting at the University of Nevada, Las Vegas, left three people and the gunman dead, a picture emerged of a quiet, lonesome academic with obsessive tendencies who was upset by being rejected for a position at the university, according to law enforcement sources, neighbors and the man’s personal website.

The shooter was identified as Anthony Polito, 67, law enforcement sources with knowledge of the investigation said.

On his personal website, Polito wrote at length about his favorite topics, rarely failing to mention membership in the Mensa society for people with high IQs.

The writings revealed an obsessive nature: hundreds of organized links to favorite articles, games, things to do in Las Vegas and more.

The website included a 109-page document of praise purportedly given by past students at a business school in North Carolina.

It also included hints of delusion. In a 2014 self-published essay, Polito — despite no expertise in the field — claimed he was the first to solve the Zodiac killer’s cryptography. “Let me first say that I have been a member of MENSA for 35 years,” he wrote, then gave credentials including “a masters degree and a doctoral degree from top-tier universities.”

He concluded: “So I am not a dumb guy!”

In another essay, about the Malaysia Airlines flight that went missing with 239 people aboard in 2014, Polito wrote baselessly that “government/media disinformation was dispersed to suppress public realization that MH370 had been hijacked” in order “to suppress the actual location of the wreckage.”

In a section of the website titled “Powerful Organzations Bent on Global Domination!” he linked to a number of conspiracy theories, including a film by Alex Jones about the “globalists’ dark agenda” and a YouTube video promoting antisemitic tropes about the Rothschild family.

On his YouTube profile, Polito subscribed to a number of conservative accounts that dabbled in conspiracy theories, including accounts associated with former President Trump, Paul Joseph Watson and Dave Rubin.

He referred to himself as “Dr. Polito” in documents, citing a doctorate in operations management from the University of Georgia.

Polito wrote that he took dozens of trips to Vegas before moving there. “Over those years, my steel trap mind collected more information and trivia about Vegas than probably anyone in this state east of I-95 (at least)!”

On Wednesday night, hours after the shooting, investigators searched his apartment in Henderson with the aid of a SWAT team.

Neighbors said Polito, older and well-dressed, had always stood out from the other younger residents in the apartment complex about eight miles from UNLV’s campus. His business attire and briefcase — along with his black license plate that read ‘KAPEESH’ — had led some of the neighbors to refer to him as “mafia dude.” He didn’t like small talk.

“He’s very quiet, lived like a hermit,” said Anthony James Carew, 42, who said Polito had been his neighbor since he moved in six years ago. “I’ve never seen the guy have a conversation with anybody.”

Roni Torres, a 27-year-old teacher, said she always parked her car next to Polito’s. She would sometimes see him sitting alone in his car when she and her boyfriend left for the gym at 3:30 in the morning.

She assumed he worked for a casino with his late hours and penchant for slacks and long-sleeved white shirts.

“He would never say hi,” she said. “I would even mention to my boyfriend that he wasn’t very friendly. He seemed very off.”

The morning of the shooting, Greg Gibson, who has lived in the complex for half a year, said he caught the man’s eye.

“He seemed agitated. That’s why I noticed him,” said Gibson, 43. “He was pacing, smoking the cigarette and looked unusual, stressed out. I was like, ‘This doesn’t look good.’”

Gibson said he gave the man a nod. The man looked back with what Gibson described as a “thousand-yard stare.”

Ellis reported from Las Vegas, and Castleman reported from Los Angeles. Times staff writer Richard Winton contributed to this report.