Aaron Alexis was a mass murderer who committed the Washington Navy Yard shooting in 2013. In total Alexis murdered 12 people. On the day of the shooting he entered the Naval Yard using a valid pass, and assembled a shotgun that he had purchased a couple of days previously, in the fourth floor bathroom of building 197. Once he emerged from the bathroom he immediately began shooting, and continued with the shotgun until he managed to murder a security guard and took his beretta semi-automatic pistol which enabled him to continue the shooting despite having run out of shotgun ammunition.
When police arrived on the scene Alexis was still firing at people on the third and fourth floors, and began to engage the police with gunfire. He wounded one police officer in the leg, and after a 30 minute shoot out Alexis was fatally shot in the head.