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 police officer, a “beloved” security guard and a senior executive with investment firm Blackstone were among four people killed Monday when a lone gunman stormed a sprawling office tower in Midtown Manhattan and opened fire.

New York City homicide detectives sought clues on Tuesday to what possessed a Las Vegas man to drive cross-country and storm into a Midtown Manhattan office tower to open fire with a military rifle, killing four people,