I heard about it on All Things Considered this afternoon, and the story was very sketchy. The Washington Post says the incident began at the White House 2:12 PM, and ended when the driver was shot and killed by police at the Capitol at 2:20 PM. There still seems to be no information what led up to all this. Apparently, the driver tried to drive through the security gate at the White House, but was stopped. She then drove down Pennsylvania Avenue and tried to crash through a barrier at the Capitol. Then she drove to a spot behind the Supreme Court, where she was shot and killed. There was a 1-year-old infant in the car.
Sad story.

-Joe-