The alleged gunman was identified as 27-year-old Shane Tamura, of Nevada. Police said the motive for the shooting remains under investigation and investigators are working to understand why the suspect targeted the commercial building.

A gunman who killed four people inside a Manhattan office tower blamed his mental health problems on the National Football League and intended to target its headquarters but took the wrong elevator, officials said Tuesday.

The gunman in the deadly shooting at a New York City office tower had a background in casino surveillance and once held a private security guard license

The 27-year-old man who shot and killed four people at a Midtown office building on Monday carried a note in his pocket, police sources told ABC News.

The gunman accused of killing four people in New York City suspected he had chronic traumatic encephalopathy, or CTE — a degenerative brain disease often associated with football players.

Shane Tamura, the suspect in the deadly shooting in Midtown Manhattan, carried a note in his pocket claiming he suffered from CTE and also made references to the NFL, police sources told ABC News.