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. Here's what we know about the four people killed:

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 attorney for the man who sold what would become the deadly weapon in a mass shooting in New York City earlier this week said his client legally sold his co-worker the gun.

A man who killed four people at a Manhattan office building bought the rifle he used in the attack, and the car he drove across country, from his supervisor at a Las Vegas casino, authorities said Wednesday.