I can relate to your surprise and disbelief, because 3 or 4 years ago I would have thought what happened to Eric Garner, Mike Brown, and Trayvon Martin was against the law. Boy was I wrong.
In America, its too easy to get away with murder, all you have to say is you feared for your life. You don't even have to be 100% sure, it just can't be intentional. The laws in America allows unarmed people to get killed. Now you put a bad cop in the mix, and a lot of people are ending up dead, because the laws in America are horrible.
This cop really did not have to shoot this guy, he had a warrant for child support, its not like he was an armed and dangerous fugitive that needed to be taken off the street. It was child support.