I can't see how the shooter could have any possible defense if he goes to trial, because of him leaving his home ("castle"?) and chasing after the victim on a public street and shooting him multiple times in the back (so, as he was fleeing, which I expect will be an important aspect of the case). Has it been reported what the shooter did after he shot him? Did he stop and render aid, call 911, continue chasing after the other boys... or did he just go back inside his home as if to say, "Well, that'll be the end of that... now, where's that remote?"
MAYBE if he had stayed in his home or on his own property, he might hope for some sympathy or absolvement by using the "Castle Doctrine" laws, if they even have that there. But I don't think it would apply anyway, since the boy wasn't threatening or committing any violence or even theft. But that's a moot point since he ran out of his home and into the neighborhood to fire the fatal shots.
And likewise, he'd have a hard time defending his act of shooting him not just once, but multiple times (clearly unnecessary overkill, especially since the boy wasn't attacking him or anyone.)
Which brings us to the final indefensible (imo) act by the alleged murderer, which was that he shot him in the back. There's plenty of case precedence that will hurt the defendant there, where a person shot in the back is assumed to be attempting to flee the scene, so there's no way a shooter can say he felt threatened in some way by the victim who, had he not shot him dead, would have been off and away and no threat to the shooter in literally the next minute.
Not to mention the fact that the victim was an 11 year old child... how much of a threat could he possibly be to this grown man anyway?
Lot of bad decisions that night made by the adult who shot and killed a kid for nothing, imo.