As I said, it does appear that the cops shoot very quickly. But, again, i'd consider this a training issue, certainly nothing criminal about it.
The time from when the police car stops and when the boy is dead on the ground is about 2 seconds. There was no time to warn the boy. There was no attempt to deal with the situation peacefully. The car rolled up and the officer shot and killed a 12 year old. That calls for more than just additional training.