Sen. Bob Casey (D., Pa.) was outside the U.S. Capitol on Thursday when the day's dramatic events unfolded before him.
First there was a car chase, which he initially thought was a motorcade. Then there were gunshots - "three or four pops," Casey said.
Outside the Dirksen Senate Office building, about a block and a half from where he was standing, he saw two people "just hit the deck."
Casey had just left a lunch for Senate Democrats when the incident spilled onto Constitution Avenue, on the north side of the Capitol. He was walking to nearby Senate offices with two colleagues, Sens. Sherrod Brown (D., Ohio) and Jeff Merkley (D., Ore.).