Wish they'd mention what firearm was used - it sounded like a smaller caliber - but how the hell did he manage to get it past security checks? The #2A nuts will eat this up!
1). You can't tell the caliber from the audio on the TV.
2). He didn't get a rifle into the venue - he was on a roof outside.
3). He still should have been spotted in the prone position, in cammies, on a roof, with a long gun.