We're still in that early period when we should treat all reports as tentative. But we're getting the first outlines of what appears to have happened. We have multiple major news organization reports that the incident began when a women tried to ram the White House gates. That led to a car chase to the Capitol, with the Secret Service in pursuit, which ended with the woman being killed, presumably in the gunfire that started the lockdown at Capitol Hill.
TPM has not been able to independently confirm what appears to be the White House part of the story.
3:34 pm - conflicting reports on the suspect's condition.