LAS VEGAS (AP) -- The man who stormed a Manhattan office tower with a gun, killing four people before killing himself, worked in the surveillance department of a Las Vegas casino, part of an industry built on watching for threats before they unfold.

Shane Tamura, 27, didn't show up to work his usual shift Sunday at the Horseshoe Las Vegas. Instead, authorities say, he got in his car and drove across the country to carry out a mass shooting inside the skyscraper that houses the National Football League's headquarters. A fifth person, an NFL employee, was wounded in the Monday attack.

As investigators work to uncover a motive, questions are being raised about how a man with a documented history of mental health problems -- and a recent arrest for erratic behavior at another casino -- ended up working in one of the most security-sensitive jobs in Las Vegas.

Caesars Entertainment, which owns the Horseshoe, confirmed Tamura's employment but has yet to disclose the nature of his role or whether he was authorized to carry a weapon. A spokesperson didn't respond to emails asking whether Tamura's job required him to hold a valid work card from the state Private Investigator's Licensing Board, which is needed to work as a private security officer in Nevada.

State licensing records show Tamura previously held a state-issued license as a private security officer, though it had expired in December.

While he held that license, Tamura was arrested at a casino in suburban Las Vegas. A report on the September 2023 arrest says he was asked to leave after he became agitated with casino security and employees who asked him for his ID, and he was arrested on a misdemeanor trespassing charge. Prosecutors later dismissed the case.

Tamura had a history of mental illness, police said without giving details. Authorities have not provided more specific information about Tamura's psychiatric history but are investigating claims he included in a handwritten note he left behind, in which he said he had chronic traumatic encephalopathy, or CTE, a degenerative brain disease linked to repeated head trauma.

Officials said he had intended to target the offices of the NFL, which he accused of hiding the dangers of brain injuries linked to contact sports, but he took the wrong elevator.

Tamura's family members did not respond to messages seeking comment. No one answered a knock at the door of his family's Las Vegas home on Monday.

Tamura didn't play professional football but was a standout running back during his high school years in Southern California, where he was born, according to local news accounts at the time, including one that described his abilities as "lightning in a bottle."

One of his former coaches, Walter Roby, said he did not remember Tamura sustaining any head injuries in his playing days. He recalled an ankle injury, "but that was the extent of it."

"He was a quiet dude, soft spoken, humble and led by his work ethic more than anything else," Roby told The Associated Press. "His actions on the field were dynamic."

Some of Tamura's former classmates seemed stunned by the shooting, and several said they had lost contact with him.

But numerous others who say they were in Tamura's grade at Golden Valley High School, which has over 2,000 students, weren't familiar with him. Some of Tamura's neighbors in Las Vegas also said they didn't recognize him after seeing his photo shared in news reports about the shooting.

"They were so unremarkable, or maybe they were never home when I was home," neighbor Wendy Malnak said about Tamura and his family.

Malnak, whose house is diagonal across from Tamura's, has lived in the neighborhood since 2022. She said many of the residents on what she described as a quiet street keep in touch regularly and look out for each other, and yet none of them seemed to notice Tamura or his family before police officers showed up Monday night and surrounded their house.

Las Vegas police said Tuesday they were "supporting the NYPD with their investigation" but have not released details about the police activity Monday at Tamura's home. Two groups of New York City detectives were on their way to Las Vegas to conduct interviews and search the home, New York City Police Commissioner Jessica Tisch said.

Authorities said they were also questioning an associate of Tamura who bought a component of the AR-15-style assault rifle used in the attack. Tisch said Tamura had "assembled" the weapon and used his concealed carry permit to purchase another firearm, a revolver, last month.

"This is part of a larger effort to trace Mr. Tamura's steps from Las Vegas to New York City," she said.

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Mustian reported from New York. Associated Press journalist Safiyah Riddle contributed from Montgomery, Alabama.