The New York City office building that was the site of a mass shooting Monday had significant security measures in place.

A shooting Monday at an office building in New York City that is home to the Blackstone investment firm and the NFL left four people dead, including an NYPD officer.

A gunman who opened fire in a Midtown Manhattan skyscraper later died of a self-inflicted gunshot wound, police said. Officials say investigators recovered a note in which appeared to blame his own traumatic head injury on the National Football League,

The man who killed four people in the New York City skyscraper that is home to NFL headquarters carried a note blaming the league for his mental health problems

The gunman who opened fire in midtown Manhattan on Monday, killing four people before turning the gun on himself, left a note mentioning “CTE” several times, officials familiar with the investigation told NBC News.