A few more details from the Washington Post:
The D.C. police spokesperson said no one was struck by the bullets.
Eva Malecki, the communications director for the U.S. Capitol Police, said at a press conference that the shots were fired in the process of an arrest. It was not clear who had fired the shots and Malecki did not specify.
“During the attempt to arrest the suspect shots were fired,” Malecki said. She said an investigation is underway. Malecki said the incident involved a woman.
“Although preliminary,” she said, the incident “appears to be criminal with no nexus (sic) to terrorism.” She said the U.S. Capitol remains open. She also said there is “no sense of motive.”
Cable and print reports indicate the car was driving erratically when police tried to stop the vehicle. WUSA’s report claims the as yet unidentified driver was a woman.