A man stalked through a Manhattan office tower firing a rifle, killing four people, including a New York City police officer, and wounding a fifth before taking his own life, officials said.

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.

The man who opened fire in a Midtown Manhattan office building, killing four people and wounding a fifth, appeared to be targeting the NFL headquarters and had a note claiming he suffered from CTE, police sources told ABC News.