Tragic: Las Vegas shooting

We now know who's responsible for the massacre in Las Vegas and how it happened. But we may never get an answer to the most pressing question: why.

 Why would a 64-year-old retired accountant, with no history of violence, hole up in a casino hotel room and fire off round after round on innocent concertgoers? The carnage is almost unspeakable -- at least 59 dead and more than 500 injured. It's the deadliest mass shooting in modern American history.

The shooter, Stephen Paddock, had amassed an arsenal of 42 firearms. Twenty-three weapons, including a handgun and multiple rifles, were found in his room at the Mandalay Bay Resort and Casino. Another 19 firearms were found in his home in nearby Mesquite, Nevada. Material used to make explosives were found in his car. Authorities still think he acted alone. His brother told reporters this was totally out of character for Paddock.

And now, we're learning about the victims: people like Sonny Melton, 29, a registered nurse from Tennessee, whose wife said he saved her life before he was shot, and Rachael Parker, 33, a records tech for a police department in California.