This is still a breaking news story, with not much information yet on the shooters:
A man brandishing an assault rifle, shotgun and handgun opened fire Monday inside a building at the Washington Navy Yard — killing at least four people and wounding at least eight more, including two police officers, authorities said.
SWAT officers swarmed the building, the headquarters of the Naval Sea Systems Command, and a shooter there was killed, sources told NBC News.
The Washington police chief said there could be as many as two other shooters at large, one white and one black, both in military-style uniforms. But there was no confirmation of more than one person firing shots. Federal officials said the information appeared to be based on eyewitness reports and surveillance footage.
President Barack Obama said the rampage targeted patriots, military and civilian alike, “men and women who were going to work, doing their job, protecting all of us.”
I hope that there aren't more casualties and the perpetrators have been caught. Why do you think someone would do this?