again, the gun control debate is, again, front and center in our country right now. the president addressing the nation for the 15th time following a mass shooting since he's been president. john? >> ana cabrera for us in roseburg, thanks so much. obviously, right now a huge question today as the investigation is very much under way as we speak, is why, the investigation into the shooter and what could possibly be the motive behind something as horrific as this is happening right now. let's -- for much more on that, let's go over to debora, who has been following that. >> we're learning more about the shooter. right now it's just beginning to emerge as to who he was. let's take a quick look about what we do know about him. first of all, 26-year-old christopher harper mercer. investigators linked him to the college in to ways. first, an e-mail address to the college. second, a college theater group in which he's listed as production assistant on an upcoming production.