It looks like this guy is taking selfies with his kid
Watching the live stream I noticed their were parts that looked staged and parts that looked real. This made me think of a possible way this went down and could be how others have happened.
Most the time there are drills scheduled which I think may have been the case with this shooting. Everyone thinks they are taking part in the drill. The shooter would know it is not a drill. The guns are loaded with some blanks and some real bullets. In the video once he goes back to the car and switches guns the shots look real. This would explain why he goes back in to the piles of "DEAD" victims and starts shooting them instead of leaving to avoid being caught by police. Everyone lays there not knowing people are really being shot then.
I'm not talking about the shots while in the car. After the first round of shooting he goes out to the car and switches guns. He then goes back into the same part and starts shooting the piles of people. This time you can see where it looks like they are being hit with the shots. I think the second gun had real bullets and the first one was just blanks so people would not realize what was going on and just stay put.
Think about Newtown they said the timing and accuracy the person had was that of a military trained person. If all your targets are not running makes it extremely possible.
In the live stream the first time he enters there is a magazine laying in the hall and he comes back and picks it up and loads it after he finishes the first clip