The US Capitol is in lock down after shots were heard Thursday afternoon. ABC's Jeff Zeleny reports he's talked to three senators who told him that they in fact heard gunshots outside of the Capitol building around the Dirksen Senate Office Building...just to give you a sense of where that is just across from the street from the Capitol. And Sen. Bob Casey of Pennsylvania said he heard three pops. Didn't think they were gunfire at first but Sen. Sherod Brown of Ohio walking nearby said he knew they were gunshots initially. He said there was all types of commotion after that. Senator Jeff Flake of Arizona confirmed the account, also heard shots. These senators we're told were told to get behind vehicles so they hid in place for a while and then were brought back in to the capitol.