Apparently it's a little more complicated than that. The kids (13 & 14) didn't actually steal the car, they were unarmed, and running away from the scene when the man chased them down firing 11 shots into their backs, killing one of them.
A Sergeant in the military should know better than to shoot unarmed children in the back while they are fleeing an attempted robbery, and so a jury of his peers found him guilty on multiple counts and the judge handed down the lightest sentence she could.
The issue is that the trained military white guy snapped because the kids were black... he probably wouldn't have shot them had they'd been white and so he may have been charged with a hate crime (not sure about that?)... At any rate, not justifying any of it, it's just that nowadays if you're a white guy with a gun and you play stupid games, you can expect to win stupid prizes