True. But since the gun was found next to Pat Pat, I do not think the threat was neutralized before he was shot.
Also, there is a finite reaction time. If you wait until police are about to shoot you to drop the gun, there may not be enough time to recall an action their motor cortex is already in the process of initiating.
It's worse than that. Once the decision has been made to shoot we focus in the task of putting rounds on target. Our ability to determine that the threat has been neutralized is seriously impaired. This is just how the human mind works in life-and-death circumstances and not a failing of the shooter.