NEW YORK — A man who killed four people at a Manhattan office building bought the rifle he used in the attack and the car he drove across the country from his supervisor at a Las Vegas casino, authorities said Wednesday.

Shane Tamura, 27, fatally shot three people Monday in the building lobby before taking an elevator to the 33rd floor, killing a fourth person and then ending his own life, according to police. The building houses the National Football League’s headquarters and other corporate offices.

In a note found on his body, Tamura assailed the NFL’s handling of concerns about chronic traumatic encephalopathy, and the former high school football player claimed he himself had the degenerative brain disease, according to police. Known as CTE, it has been linked to concussions and other head trauma.

At Tamura’s Las Vegas studio apartment, investigators found a note with a different troubled message, police said Wednesday. They said the note expressed a feeling that Tamura’s parents were disappointed in him and included an apology to his mother.

Police said they also found a psychiatric medication, an epilepsy drug and an anti-inflammatory that had been prescribed to Tamura.

Investigating his movements as well as his mindset, detectives learned that he purchased the rifle and car from his supervisor at a job in the surveillance department at the Horseshoe Las Vegas, the New York Police Department said.

The supervisor legally bought the AR-15-style rifle he sold to Tamura for $1,400, police said, adding that they had erred in saying earlier that the supervisor supplied only parts of the rifle. It wasn’t immediately clear whether the gun sale was legal.

Police didn’t identify the supervisor, who has been forthcoming with them and hasn’t been charged with any crimes. Tamura had alluded to him, apologetically, in the note found in the gunman’s wallet after the rampage, police said.

Victims’ funerals begin

As investigators worked in both New York and Las Vegas, one of the victims, real estate firm worker Julia Hyman, was buried Wednesday after a packed, emotional service at a Manhattan synagogue.

Her uncle, Rob Pittman, said the 27-year-old Bronx native lived “with wide open eyes” and “courage and conviction.”

Hyman had worked since November at Rudin Management, which owns the building and has offices on the 33rd floor. A 2020 graduate of Cornell University, she had been the captain of Riverdale Country School’s soccer, swimming and lacrosse teams in her senior year, school officials said.

Relatives and colleagues of another victim, security guard Aland Etienne, remembered him at a gathering at his union’s office. The unarmed Etienne was shot as he manned the lobby security desk.

“We lost a hero,” younger brother Smith Etienne said. “He didn’t wear no cape. Had no fancy gear. He wore a security officer’s uniform.”

Police were preparing for a funeral Thursday for New York City police officer Didarul Islam. A member of the force for over three years, he was killed while working, in uniform, at a department-approved second job providing security for the building.

Funeral arrangements for the fourth victim, investment firm executive Wesley LePatner, haven’t been made public.

An NFL employee who was badly wounded in the attack is expected to survive.

Detectives scour for clues in Las Vegas

Teams of New York City detectives continued working Wednesday in Las Vegas, where they had a warrant to search Tamura’s locker at the Horseshoe casino and were awaiting warrants to search his phone and laptop, police said. They also planned to speak to his parents.

Besides the note and medication at his apartment, they found a tripod for his rifle, a box for a revolver that was found in his car in New York, and some ammunition for both guns, the police department said.

Police have said Tamura had a history of mental illness, but they haven’t given details. In September 2023, he was arrested on a misdemeanor trespassing charge after allegedly being told to leave a suburban Las Vegas casino and becoming agitated at being asked for his ID. Prosecutors later dismissed the case.

His psychiatric history would not have prevented him from legally purchasing the revolver just last month.

Nevada is among 21 states with a red-flag law that allows for weapons to be taken from people if courts determine they pose a risk to themselves or others. First, relatives or law enforcement must seek a so-called extreme risk protection order.

A new state law, effective this month, also lets officers confiscate firearms in the immediate vicinity of someone placed on a mental health crisis hold.

“These laws only work if someone makes use of them,” said Lindsay Nichols, policy director of the Giffords Law Center to Prevent Gun Violence.