Trace gallagher. We are alive again tonight in las vegas, as this town begins to heal, another busy day for investigators, in a grief stricken town, as they try to shed some light on why an evening of fun and music suddenly became a scene of coldblooded murder. And to look at this video taken just seconds before the firing started, because it gives you me perspective about the witnesses who say it sounded at first like fireworks. Watch this. [screaming] trace from dancing to the rat a tat tat of bullets. Authorities are hoping that this woman can help them delve into the mind of the mass killer. She, of course, was his girlfriend. Tonight, well learn what she told the fbi about the man who took 58 lives and left hundreds of other people injured. Plus a deeper look into the killers hotel room. Startling pictures from inside his room reveal his incredible firepower, and the meticulous planning behind the bloodied rampage. Will the killers massive arsenal convince lawmakers to strengthen