 THE SUSPECT WAS SHOT AND KILLED BY THE SECRET SERVICE. HE'S BEEN IDENTIFIED AS 20-YEAR-OLD THOMAS MATTHEW CROOKS OF BETHELL PARK, PENNSYLVANIA. HIS MOTIVE IS NOT YET KNOWN. CBS NATIONAL SECURITY CONTRIBUTOR SAMANTHA VINEGRAD SAYS INVESTIGATORS HAVE A LOT OF WORK AHEAD OF THEM. Right now, the goals are to investigate the incident, both the perpetrator and the security failures, as well as to try to tamp down any