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.

Study my brain please,” read a note left by the gunman accused of killing four people in a building that houses NFL’s headquarters

Police say the gunman in the Manhattan office building shooting tried to target NFL offices. In a note found in the gunman's pocket and obtained by CBS News, he alluded to having CTE. A former high school football player,

A New York City police officer who was among the four people shot and killed by a gunman during a rampage at a Manhattan office tower will be laid to rest Thursday. Officer Didarul Islam, 36, was fatally shot Monday in a midtown building housing the National Football League’s headquarters.

Four people were killed and a fifth was injured in a mass shooting at a Midtown Manhattan office building on Monday.The injured victim was an employee at the NFL, according to NFL Commissioner Roger Goodell.