Law enforcement sources told CBS News that Las Vegas shooter Stephen Paddock is believed to have used the freight elevator at the Mandalay Bay hotel casino in the days leading up to last week's deadly attack. It wasn't clear what Paddock used the freight elevator for or how often he used it. CBS News senior investigative producer Pat Milton reports authorities were continuing to comb through Paddock's electronic devices — including a laptop and cellphone — at the FBI crime lab in Quantico, Virginia. So far, none of the devices point to a motive for the shooting rampage. Meanwhile, billboards...