Sgt. David Schlosser just gave a briefing on this afternoon’s shooting at the U.S. Holocaust Museum. Here are the key points:

*A lone gunman entered the building around 12:50 p.m. The man was armed with a long gun, and it’s unclear at this point whether it was a rifle or a shotgun.

*Shortly after entering, the gunman opened fire and at least one security officer returned fire. The shooter was wounded and is now in “pretty serious” condition, according to Schlosser.

*One of the security officers appears to have been wounded as well. No fatalities have been reported at this point.

*There is no reason to believe that another shooter is on the loose. The museum has been “cleared,” and a secondary sweep of the building is underway.

David Unruh, who came to Washington for his 47th wedding anniversary, was waiting to enter the building when he heard at least five shots. The security guards thereupon ordered everyone to hit the floor. “It was terror. We were frightened,” says Unruh, who glimpsed a large gentleman in a corner, trying to shield his children.

By Mike DeBonis