Good Lord, Tamir Rice was not ‘murdered’, he was the victim of a tragic accident. The police — who, never forget, were responding to a call about a juvenile with a gun which, although a toy, had the orange ID marks removed — were investigated with the results presented to a grand jury, who determined that there was no deliberate, malicious intent on their part (the critical attribute in a lawful charge of Murder). However, the officer in question was fired for his role in the shooting, probably the most reasonable outcome given the circumstances.
It would be helpful to our society as a whole if people weighed the actual definitions of terms such as Murder, instead of simply using them gratuitously, for the most inflammatory effect.