NEW YOEK (ABC News) — Shane Tamura, who drove cross-country from Las Vegas and opened fire at the New York headquarters of the NFL, killing four, had CTE, the New York City Office of the Chief Medical Examiner said Friday, confirming what was in the shooter’s own writings.

Police found a three-page note in Tamura’s pocket claiming he had a traumatic brain injury and blaming the NFL for “concealing the dangers to players’ brains to maximize profits.” Elsewhere, Tamura wrote, "Study my brain please. I'm sorry."

“Following a thorough assessment and extensive analysis by our neuropathology experts, OCME has found unambiguous diagnostic evidence of Chronic Traumatic Encephalopathy, also known as CTE, in the brain tissue of the decedent. The findings correspond with the classification of low-stage CTE, according to current consensus criteria,” the medical examiner’s office said. “CTE may be found in the brains of decedents with a history of repeated exposure to head trauma. The science around this condition continues to evolve, and the physical and mental manifestations of CTE remain under study.”

The medical examiner’s office previously said Tamura died by suicide of a self-inflicted gunshot. The pathologists do not say whether CTE played a role.

NYPD officer Didarul Islam was the first person shot and killed when Tamura entered 345 Park Avenue just before 6:27 p.m. Monday, July 28 and opened fire in the lobby.

Outside, thirty seconds earlier, Tamura double-parked a black BMW he purchased from his supervisor at Horseshoe casino in Las Vegas and drove 2500 miles across the country. He transported a .357 caliber handgun and an M4-style rifle

An NFL employee was shot and wounded. That individual managed to alert his coworkers before seeking help for himself, police said.

Wesley LePatner, a senior managing director at Blackstone, was shot and killed as she tried to hide behind a pillar. Tamura then shot and killed 46-year-old security guard Aland Etienne.

All of the victims in the lobby were shot in less than 30 seconds.

Tamura then moved to the elevator bank, inexplicably allowing a woman to pass unharmed, police said. Detectives believe he went looking for the NFL offices but entered the wrong elevator.

He ended up on the 33rd floor about 6:28 p.m

In that time, office cleaner Sebije Nelovic said Tamura fired at her but missed. Nelovic said in a statement sent by her union that she ran down the hall, hid in a closet and “started praying.”

She said she heard shouting, then footsteps as the gunman moved toward the closet where she was hiding.

As gunshots hit the closet door, Nelovic said she thought of Julia Hyman, the 27-year-old who often worked late in the offices of Rudin Management, the company that operates the building. “I thought, God help her,” Nelovic said.

Hyman was the last person shot and killed before Tamura killed himself approximately four minutes after arriving on the 33rd floor.

All told, police said he fired 47 rounds, a number that indicates he reloaded once.