Suspect Shane Tamura died by suicide after the Monday mass shooting at 345 Park Avenue, which is home to NFL headquarters. One page of the note found in Tamura's pocket accused the NFL of concealing the dangers to players’ brains to maximize profits, sources said.

The assault rifle used in mass shooter Shane Tamura’s deadly rampage at a Park Avenue skyscraper was assembled piece by piece – with the critical part purchased by his boss, according to officials and sources.

A police officer and three other people were shot and killed, and one other injured, by a crazed gunman who stormed a swanky Midtown skyscraper early Monday evening — before turning the gun on himself,

Shane Tamura, the Park Ave. gunman who killed an NYPD officer and three others before taking his own life, left behind a suicide note saying he suffered from CTE, a brain injury often linked to playing football, police sources said Tuesday.

In the photos first shared online, Tamura was captured walking into 345 Park Avenue with an assault rifle in his hand while decked out in a suit.

Authorities also found a vehicle with Nevada plates registered to Tamura at the scene, with a rifle case inside, sources said.

Police found a note on Shane Tamura, who shot and killed himself after the attack, claiming he suffered from CTE and asking that his brain be studied.

A gunman armed with an M4 assault rifle killed four people—including a police officer—after opening fire in broad daylight in the center of New York City, before reportedly ending his own life. The gunman was later identified as 27-year-old Shane Tamura from Las Vegas.

The suspect in a New York City shooting which left at least five people dead on Monday was identified by the New York Post.

Roger Goodell sent a letter to all NFL employees after the league office was targeted by a gunman in a mass shooting on Monday, July 28.