A shooting can be "legal" and still be unnecessary and wrong.
It may well be that the shooting of Tamir Rice was not a crime, and it may well be that the use of force was justifiable given the circumstances at the moment of the shooting. Nonetheless, it was still a preventable shooting. Now that the officer will not face criminal punishment for the shooting, the question is how to prevent this from happening again.
I will not get into whether or not the officer was legally justified in shooting Rice, but the shooting was certainly unnecessary, preventable, and should be grounds for termination of the officer involved. While the officer cannot control the fact that the dispatcher did not relay critical information about the boy (such as the fact that the 911 caller said the gun was probably fake) he can control how he responds.
We have all seen the video. The police car rolls up right next to a 12 year old boy, a police officer fires shots and the boy dies. This was not an active shooter situation. The police could have parked farther away, behind cover, and ordered Rice to drop his weapon. What if Rice actually had been a few years older, carrying a real gun and drew on the police first? They could be dead or gravely injured because they took an unnecessary risk. The driver and the shooter should have at least been disciplined (if not fired) for that reason alone.
But the "Black Lives Matter" protesters need to be very careful about what they ask for. A Twitter campaign calls for LeBron James to boycott the NBA until the federal Justice Department "imprisons the murderers of Tamir Rice." But this is a terrible idea that will cause much more harm to poor blacks than it will do to punish bad cops. The idea that the Justice Department should simply "imprison" the officer without a trial is a frightening attack on due process.
With all of the abuses we have seen in the War on Drugs and general hysteria over crime, any precedent we set in limiting due process can be guaranteed to harm poor inner city blacks first and worst. Do we really want the same system that has historically treated blacks poorly to be given more power, while the rights of suspects are further restricted? We are already seeing a backlash to the "Black Lives Matter" movement with factually false fear-mongering.
The answer is better training and more accountability within the department. We need to reject the myth that police officers are in more danger than ever (statistically, police are safer than they have been in generations) and police training should reflect that. Civilian leadership, and activist groups, should emphasize deescalation first. The federal government should stop contributing to the "warrior" mentality by giving out military equipment to local police departments. This can change for the better, but it is a long and difficult road to reform.
Above all else, we must resist calls that expand the power of the state. Giving the government even more power at the expense of the rights of citizens is emphatically not the solution to government abuse of power. That is madness.