Hell I'd be surprised if he even knew the kid was 13 until after the fact. Dark alley at 230am. As far as he knew he was pursuing an armed and dangerous suspect with a gun known to have been fired at vehicles.Sorry, he shot a kid. He had plenty of time to assess it was a small person he was chasing. You have to make sure before you shoot a human. I'd rather be dead than know I'd shot and killed a 13 year old.
I expect a lot of the police, want them held to a high standard, but my standard isn't so high as to ask them to risk letting a suspect known to have a gun and a willingness to use it potentially have the first shot in an armed confrontation.