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:

Workers in business attire were seen piling couches up against their office door -- with the towering furniture reaching the ceiling.

The executive was shot and killed in the lobby of the ritzy Park Avenue office tower when gunman Shane Tamura opened fire.