I'll lay 99.999% odds that the shooter was:
1) a convicted felon
2) illegally carrying concealed
3) involved in other illegal activity at the time of the shooting
I also will bet money that someone in the media or the anti-gun crowd will try and blame this on WalMart's pro-2A policy, and on their pro OC policies. And that they will try to pressure WalMart to disallow OC. (but it will still be OK to CC there--because, you know--if they can't see it, it doesn't exist...)
In 3....2....1....