Volkswacht Bodensee - New York mass shooter blamed NFL for his brain injuries

The revelation that the killer, identified as 27-year-old Shane Tamura, carried a note referring to the degenerative brain disease chronic traumatic encephalopathy (CTE), offered the first possible motive for the shootings late Monday that brought central Manhattan to a standstill.

The attacker shot a police officer outside the tower on Park Avenue, then opened fire in the lobby, before trying to head up to the National Football League's offices, armed with a semi-automatic rifle.

The suicide note said "that he felt he had CTE, a known brain injury for those who participated in contact sports. He appeared to have blamed the NFL for his injury," Adams told CBS News.

Adams said that Tamura had never actually played for the top professional league. However, he was reportedly a star player at high-school-level in California.

The suicide note asked that his brain be kept for examination for CTE damage, The New York Times reported.

The bloodshed sparked a massive police response in the teeming center of the city -- not far from where a man with a grievance against UnitedHealthcare gunned down the medical insurance company's CEO in broad daylight last December.

New York Police Commissioner Jessica Tisch told a news conference that Tamura had a history of mental health issues.

President Donald Trump on Tuesday called the mass shooting a "senseless act of violence" carried out by a "lunatic."

- Deadly journey -

New details emerged Tuesday about the gunman's bloody attack and final journey.

Authorities said he had driven across the country from Nevada and stopped outside the skyscraper in a black BMW, carrying a rifle.

He killed a police officer immediately, then began "spraying the lobby" with bullets," Tisch said.

A female bystander and a security guard were hit, Adams said, explaining that this prevented anyone hitting a panic button that would have stopped the elevators from working.

As the guard "attempted to hide himself behind the counter, he was killed as well, and the suspect then took the elevator upstairs," Adams said.

"If he was able to get to the button, he could have froze the elevator."

One of those shot was an NFL employee, who was "seriously injured" but stable in hospital, league commissioner Roger Goodell said in a statement to employees.

But while his target was determined to be the NFL offices, Tamura "took the wrong elevator," Adams said, ending up on the 33rd floor, which houses the building's management. He shot one person dead there and then shot himself in the chest.

Adams said the fallen police officer was a 36-year-old immigrant from Bangladesh.

Office worker Shad Sakib told AFP that he was packing his things to leave work when a public address announcement warned him and his colleagues to shelter in place. "Everyone was confused," he said.

There have been 254 mass shootings in the United States this year including Monday's incident in New York, according to the Gun Violence Archive -- which defines a mass shooting as four or more people shot.

N.Schaad--VB