Police 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.

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

Shane Tamura, a 27-year-old private investigator from Las Vegas, has been identified as the gunman behind Monday's Midtown Manhattan shooting.