Several governmental buildings in Washington, D.C., were evacuated Thursday morning due to what Capitol Police call “an active bomb threat investigation” after a man drove a pickup truck onto a sidewalk.

Law enforcement negotiators are working to make contact with the person in the vehicle, law enforcement sources told ABC News.

Negotiation is still ongoing to have a “peaceful resolution” and the suspect’s motives were unknown, Capitol Police Chief J. Thomas Manger said in a press conference around noon local time.

The suspect told responding officers he had a bomb, and responding officers said he had what appeared to be a detonator in his hand, Manger said.

Authorities are also investigating a video posted to Facebook that purports to have been posted by the man in the vehicle.