Let us look at the bigger problem….Sammy apparently was diagnosed with Schizophrenia.
So, do we continue to bitch about the cops? Or do we put some more effort on dealing with what the actual problem is, the failing of our mental health system? Sure the cops may have made mistakes and there will be more then enough hand wringing over their actions. But far greater failures occurred prior to this 15 year old being aboard a street car.
People fall through the medical system cracks all the time for all sorts of reasons physical and mental. Sometimes people delay getting help or they don't follow through on physicians orders. In other cases these psychotic episodes are a result of drug use. Surely you're not advocating that if the medical system fails someone then they can expect to be peppered with lead from some small dick cop.
Maybe Sammy in a moment of clarity decided he couldn't take the pain he felt his ilness was causing him anymore and wanted a way out.
Let me add to your conjecture. Maybe the cops are still pissed the guy who killed one of their own using a snowplow got off using the insanity defence and vowed to never let it happen again.