New York City Mayor Eric Adams on Tuesday said the gunman who killed four people inside a Manhattan office building was trying to target employees at the NFL’s headquarters, but wound up taking the wrong elevator.

Authorities said the shooter, 27-year-old Shane Tamura, had a note claiming he suffered from chronic traumatic encephalopathy, or CTE, a brain disease associated with blows to the head from contact sports such as football.

Hundreds of former NFL players have been diagnosed with the disease, which can be determined only after death.

Tamura played football while growing up in Southern California, according to media reports. His note said he wanted his brain to be studied for the disease after his death, according to The Associated Press.

“He seemed to have blamed the NFL,” Mr. Adams said in an interview with New York’s WPIX. “The NFL headquarters was located in the building, and he mistakenly went up the wrong elevator bank.”

Tamura, who police said drove from Las Vegas to Manhattan, took the lift up to the 33rd floor. The NFL’s headquarters are located on the fifth floor of the tower that also houses the financial companies Blackstone and KPMG.

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The killer’s grievance offers a potential motive for why police said he fatally shot four people Monday night inside the Midtown skyscraper.

Authorities said the victims included NYPD Officer Didarul Islam, who was off duty but in uniform while working security.

Local media reports identified the two slain women as Wesley LePatner, an executive who handled Blackstone’s real estate fund, and Cornell University graduate Julia Hyman.

Officials haven’t shared the identity of the other male security guard working on the ground floor.

“I trust our Law Enforcement Agencies to get to the bottom of why this crazed lunatic committed such a senseless act of violence,” President Trump wrote Tuesday on Truth Social. “My heart is with the families of the four people who were killed, including the NYPD Officer, who made the ultimate sacrifice.”

NYPD Commissioner Jessica Tisch said Tamura’s rampage began at about 6:30 p.m. Monday when he carried an M4 rifle into the building’s lobby and immediately sprayed bullets.

Three of the victims were mortally wounded in that part of the building, with another man left in critical condition.

Police said the gunman then took the elevator up to Rudin Management’s offices on the 33rd floor, where local reports said he killed Ms. Hyman.

Tamura ended his life by shooting himself in the chest shortly afterward. Authorities said his ID and a concealed carry permit from Las Vegas were found on him.

Las Vegas police shared that Tamura had a history of mental health issues, and New York police spotted medication in his car, Ms. Tisch said, but she didn’t specify what the conditions were or what medication was seized by police.

Officials said Officer Islam, 36, was a Bangladeshi immigrant who had been serving in the department for nearly four years when the deadly shots rang out. He leaves behind his pregnant wife and two boys.

“He was doing the job that we asked him to do. He put himself in harm’s way. He made the ultimate sacrifice,” Ms. Tisch said. “He died as he lived: a hero.”

• This story is based in part on wire service reports.

• Matt Delaney can be reached at mdelaney@washingtontimes.com.