good post...I was thinking the same the same thing! After a while, there were hundreds of people behind him, right? All it took was one guy in the bunch of people nearby to jump on his back and choke him out in 10 seconds....or snap his neck.
I have not heard or read anything that suggested that. If anything, the shooter planned his position carefully.
Mass confusion, movie playing the entire time, dark theater, overwhelming noise and tear gas.