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."

Multiple casualties as gunman opened fire in the lobby of the midtown Manhattan building on Park Avenue that is home to the Blackstone investment firm and other corporations before moving to other floors.

Didarul Islam, 36, was a father of two, with a third on the way, and was working a second job as a security guard at the building where shots rang out.

A gunman who killed four people when he stormed a skyscraper in the heart of New York on Monday evening left a note that appeared to blame the National Football League (NFL) for a brain injury, the city's Mayor Eric Adams has said.