Police have identified the gunman as Shane Tamura, a 27-year old former high school football player, who authorities say drove from his home in Las Vegas to Manhattan because he believed he had a brain disease linked to contact sports and accused the NFL of hiding the dangers of playing football.

A gunman who had traveled across the country strode into a Manhattan office tower Monday and opened fire, killing four people – including a police officer. The motive for the shooting at a building that houses the headquarters of the NFL,