The man who stalked through a New York City skyscraper firing a rifle tried to target the National Football League headquarters but took the wrong elevator, Mayor Eric Adams said. The gunman killed four people including a New York City police officer and wounded a fifth before taking his own life Monday evening,

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.

A note found in the gunman's wallet was critical of the NFL and mentioned CTE. The 27-year-old wrote, “Study my brain please. I’m sorry."