It is hard to say only Ersland knows what his true intent was that day but from what you can see it looks like he basically finished that kid off in cold blood.According to many states you must be in danger of attack and have no other option but to use deadly force once the threat is gone you cant.It also looks like Ersland may have even been able to see that the kid he shot was not even armed his hands are on his head(in surprise I dont think he is trying to give up) when he gets hit.While there the other kid is plan as day aiming a weapon at him yet Ersland shots the other first
.Ersland got lucky that the other kid ran because he could have easily flanked and killed Ersland who was still focused on the kid that he later shots again.