Cops are trained to shoot center mass (at the vital organs) and to keep shooting until the threat is stopped. The fact that this is one of the best ways to kill someone is incidental to stopping the threat.

Every single self defense trial where a prosecutor tries to argue that the defendent should have been able to calibrate his use of force to the exact moment that they believe (after the fact) that it was no longer needed should have the local police's use of force procedures thrown right back in their face.