The Census Bureau confirmed on Twitter that there had been "an incident at the Suitland Federal Center and there is an ongoing investigation."
The guard was in "extremely critical" condition after being shot at least once in his upper body at the Census Bureau's suburban Washington headquarters in Suitland, Maryland, Prince George's County Fire Department spokesman Mark Brady said in the Washington Post.
A chase and shootout ensued and the suspect was later shot in the head in Washington's popular H Street neighborhood known for its nightlife, the Post reported.