Yeah, I would have thought the circumstances were involuntary manslaughter or some kind of negligence at least too, because by the end result it's fairly obvious that something went horribly wrong and a kid ended up dead. But I've read a news article that explained that this US state (like many apparently) has special laws to protect police officers killing people that go way beyond regular self-defense laws, so that they are allowed not only to shoot when they are objectively threatened but also when they just think they are threatened, and also allowed to shoot fleeing people when they think they are criminals who might escape (which I find horrifying) and such. So basically it seems that if someone stays put the officer can always claim that something felt threatening and if they run away they can claim that they thought they were a criminal, and it only needs to be in the officer's head, nothing real.

So I guess short of an officer confessing to a murder plan beforehand on video and then witnesses (preferably not black ones nor ones connected to the victim in any way that might bias them) confirming that the unarmed victim really didn't do anything that could be perceived as threatening, there really is no way they can be convicted of anything, because it's not like you can prove that someone didn't feel threatened.