I won't go into details - you can find those. I'm going to speculation on motivation of the shooter.
My first thoughts were that this was some sort of Jihadist fantastist - considering they were withholding his name while putting out names of victims. Then - not. Honestly, I'd almost wish he was - it'd make explaining it all easier to frame it in the terms of Islamic fanaticism.
My second thoughts are that this is some asshole with dreams of notorious fame. As some say - pop culture's a cesspool. You've got subcultures that glorify intentional, studied ignorance, violence and misogyny.
Yet... there will be those who will blame the right. They'll be making pronouncements about the right-wing conservatives being the focus of ignorance, violence and intolerance - and that it's their attitudes which are causing the problem. (Look at how fast folks were to connect Giffords' shooting with Palin's website - despite there being no evidence that the nutcase who did it was even politically aligned in any direction at the time, and well over a year later there still isn't.)
But all you've got to do is look at the violence that the Tea Party's not fallen into, and you'll see a slight problem with that. Yet the wonderous Occupy movement's been plagued by violence...
You'd almost think there was a problem there.
On the right, they're looking to establish a framework that proves a structure for society, something stable and predictable they can live their lives in. They understand that personal freedom requires personal responsibility, and that uncoupling the two isn't going to yield a good result in the long run.
Yet it seems like all too many want to tear any sort of framework apart because they dislike any expectations that they show some sort of self-control. They don't like the imposition of (to them) distasteful cultural norms on their wants and desires. They want to party - they don't want to show up for work. They want things given to them, without limit - yet are unwilling to work to provide for others. They want freedom, but don't want responsibility. They want the structure to shelter them, but they're not going to do a damn thing to help build it.
Perhaps there's only so much of that any one civilization can take...
We'll likely find out soon enough what his 'motivation' was. There'll be something found on Youtube, or Facebook - or something will be leaked from the press. Maybe he had a bad childhood, maybe he's reacting to a breakup with his girl. Maybe he flunked summer school, and was angry. Maybe he played too many video games.
For whatever reason - he's a murderer. Deliberately committing premediated murder. This wasn't a random, impulsive act.
And though I'm curious about his motiviation - it won't excuse his action.