The gunman, who said in a note he believed he had CTE, targeted skyscraper that houses the NFL's headquarters.

Wearing body armor and wielding an assault-style rifle, the alleged gunman burst into a Midtown Manhattan office building shooting victims at random.

Investigators are combing through evidence in the wake of New York City’s deadliest mass shooting since 2000, trying to figure out more about the gunman who unleashed an assault-style rifle in Midtown,

Tamura was involuntarily held after being considered a danger to himself or others, according to a law-enforcement official.

P olice have identified the man who they say entered a Midtown Manhattan office building wearing body armor and opened fire, killing four people with a high-powered rifle, as Shane Devon Tamura.

Shane Tamura, a 27-year-old man from Las Vegas, has been identified by the NYPD as the shooter who killed four people inside a Manhattan skyscraper on Monday. Tamura left his home on Saturday for a three-day cross-country journey,

Investigators found the note in the wallet of 27-year-old shooter Shane Tamura who police said opened fire inside of 345 Park Avenue.

No motive has been announced. A suicide note was found expressing grievances with the NFL and saying Tamura suffered from CTE, a source said. Follow for live updates.