The law was not thrown out.
You have a right to your opinion, but not your own facts.
Did you follow the trial at all? Even if we accept that Rosenbaum was trying to take the gun; which is questionable, was it really necessary to shoot him 4 times? Was KR about to die at Rosenbaum's hand? Was deadly force his only reasonable option to repel the alleged attack?
Did you see the KR interview with TC? KR admitted he pointed his rifle at at Grosskreutz first. He did not fire at that point because Grosskreutz backed off.
Grosskreutz then raised the gun in response to something KR did and KR fired.
KR said he pointed the weapon at several others who approached, but did not shoot because they backed off. Were these others about to kill him too?
I think KR was defending himself. I am not sold that deadly force was necessary.