It sounds like he had opportunity for a warning shot. Yet when the kid laughed at his his jammed gun and didn't run what did he think? This guy is wacked? and shot him.
However, shooting a second time in the face because the kid laughed at you, is not even close to protecting your home. But it's like when cops beat up suspects after a chase. It's wrong but it happens, there is a psychological reason for it, and no it is not "because they are racist or bullies or love to beat up people".
That being said this guy murdered that girl and should be punished. He went too far. You don't put a person "out of thier misery" like you would a wounded animal. You call 911 and get an ambulance over ASAP.
It is rather pathetic how the article paints these two criminals who are ultimately responsible for thier own deaths because it was thier own actions which led to the shootings.