Police have identified the man who they say entered a Midtown Manhattan office building wearing body armor and opened fire, killing four people with a high-powered rifle, as Shane Devon Tamura.

The 27-year-old recently lived in Las Vegas, where he was issued a concealed firearms permit by the Las Vegas Police Department. He was previously issued a work card by the Nevada Private Investigators Licensing Board, which has since expired, according to records reviewed by ABC News. His last known address was in a gated community in Las Vegas.

MORE: 4 dead, including off-duty NYPD police officer, in Midtown Manhattan shooting: Officials

Tamura worked as a surveillance department employee at the Horseshoe hotel and casino in Las Vegas, a spokesperson for the Horseshoe said on Tuesday.

Several squad cars from the Las Vegas Metro Police were seen at the entrances to a gated neighborhood where Tamura was believed to have lived.

Spencer Platt/Getty Images - PHOTO: Active Shooter Shuts Down New York's Park Ave As Injuries Are Reported

He completed high school in the Los Angeles area, where he was a competitive football player, according to a school official who spoke with ABC News. Caleb Clarke, who said he was a former classmate of Tamura in high school, described him as a "goofball" and did not recall him having any mental health issues. Tamura was a running back with Grenada Hills Charter for a portion of his high school career, but did not play professionally.

ABC News - PHOTO: Midtown Manhattan suspected shooter Shane Tamura.

Investigators are analyzing a note found in Tamura's pocket claiming he suffered from chronic traumatic encephalopathy (CTE) and asking that his brain be studied, police sources told ABC News.

CTE is a brain disease linked to repeated hits to the head, often seen in military veterans and athletes, including football players, hockey players and boxers.

"We have reason to believe he was focused on the NFL agency that was located in the building," New York City Mayor Eric Adams said on Tuesday in an interview with MSNBC.

The Park Avenue office building targeted in the attack houses the headquarters of the National Football League as well as several other major businesses.

"He appeared to have blamed the NFL for his injury," Adams told CBS on Tuesday.

It remains unknown if Tamura suffered from CTE, which can't be diagnosed in a living person with certainty, but doctors may suspect it based on symptoms and a history of head trauma.

New York Police Commissioner Jessica Tisch said Tamura had a "documented mental health history."

Law enforcement sources told ABC News that Tamura had two mental health crisis holds in his background in Nevada, one in 2022 and the other in 2024. Those holds typically allow a person to be detained for up to 72 hours if they are thought to be a danger to themselves or others.

Tamura was arrested in September 2023 on suspicion of trespassing at the Red Rock Casino Resort & Spa in Las Vegas, according to a police report from the Las Vegas Metropolitan Police Department.

Tamura, according to the police report, refused to provide identification when he attempted to collect $5,000 in winnings at the casino. When employees asked him to leave, he refused to budge without his money, and a police officer took him into custody when he saw an "agitated" Tamura allegedly grab a casino security officer, become "obstructive" and refuse to comply with commands from officers trying to detain him, according to the report. In November 2023, the charge against Tamura was dropped when the Clark County District Attorney declined to file a complaint.

Investigators believe Tamura left his Las Vegas home on Saturday and began driving to New York City in a black BMW packed with guns and ammunition, officials said. The initial investigation shows his vehicle traveled through Colorado on July 26, then Nebraska and Iowa on July 27, and then in Columbia, New Jersey.

ABC News - PHOTO: A police officer and a civilian were shot in Midtown Manhattan on Monday by a suspect who fled into an office building, police sources told ABC News.

He arrived around 6:30 p.m. at the 44-story office building at 345 Park Ave. in Midtown Manhattan, police said.

After entering 345 Park Ave. and "spraying it with gunfire" and killing three people, including off-duty NYPD Officer Didarul Islam, who is working security at the building, and a building security officer, identified by his union as Aland Etienne, authorities said.

Before getting on an elevator, surveillance video captured Tamura allowing a woman to walk out of the elevator, sparing her from being shot, Adams said.

Tamura then allegedly took the elevator to the offices of real estate management firm Rudin Management on the 33rd floor, where he shot and killed one additional person. Tamura was found dead from what is believed to be a self-inflicted gunshot wound, officials said.

“As New Yorkers, we stand shoulder to shoulder in the face of this hatred, we grieve with the families and loved ones of those lost, and we pray for the full recovery of those injured,” the Rudin family said in a statement released on Tuesday.

The company added, “The Rudin family and everyone at our company are devastated by yesterday's senseless tragedy. Our thoughts and prayers are with those injured and lost last night, including our cherished Rudin colleague, a brave New York City police officer, a beloved lobby security guard and an employee at a tenant firm."

ABC News has reached out to Rudin Management for comment. Police have not identified why he went to that floor or if he has any connection to the company.

"His motives are still under investigation, and we are working to understand why he targeted this particular location," Tisch said.