if he could go back to work today. >> reporter: tonight the biggest mystery continues to swirl. >> to me, the biggest mystery is the motive. i mean it's just very odd that we don't know why. when we look at not just mass shootings but anything, we generally know what the motive is fairly quickly. and the mystery to me is that here we are almost two weeks out, and we have no idea why this guy did this. i think that he didn't want us to know the motive. otherwise, we would have found it out by now. >> reporter: but investigators are still doggedly trying to piece that possible motive together. the sheriff saying they're trying to establish a timeline of stephen paddock's life and everyone he was ever associated with. wolf. >> brian, that might even include his late fact, who was a convicted bank robber, right? >> reporter: today "the new york times" posted a psychiatric evaluation that was conducted on the father in a phoenix jail in 1960. the evaluator concluded that benjamin paddock, pictured here,