i watched that video the other day . it shows nothing. all you hear is the driver say he a gun, the officer say ok , then say don't touch the gun.. then him screaming don't touch the gun then shooting...
I watched the same video. If I remember correctly, the officer did not have a body camera. The only significant information comes from the sound track. Initially, the officer seems comfortable with Castile's being legally armed. Then, the tone of his voice changes to alarm followed by panic. Unless the officer was already lying during the incident, Castile did something consistent with drawing his gun and was shot for it. We don't know what that was. Maybe, he was reaching for his wallet and the officer thought it was his gun. Maybe, his gun fell out of his pocket and he grabbed for it.
If I found myself in Castile's position, I would tell the officer exactly where my gun was located. If compliance with his orders required reaching anywhere near it, I would warn him about that and seek confirmation that he wanted me to proceed anyway.
Misinterpretations of behavior can have fatal consequences. Gary Young's class on the law of use of force had two examples. One was the shooting of Amadou Diallo in New York. He ran from a group of strange men who chased him. His pursuers were plain clothes police who thought he was a rape suspect trying to escape. When he pulled out his wallet, they thought it was a gun and shot him to death. It didn't help that one of the officers tripped and fell which led the others to believe he had been shot. The other example was a man who returned home to find two strangers inside. When they approached him aggressively, he shot both. It turned out they were delivering a washer and dryer after normal business hours at his wife's insistence. (I suspect their aggression stemmed from annoyance at being made to work late.) Both incidents were bad shootings in the sense that innocent people died. But they resulted from mistakes rather than criminal intent. The shooters jumped to incorrect conclusions at the beginning and misinterpreted the victims' subsequent actions as confirmation of those conclusions.
The law does not require your decisions to be infallible. It requires them to be reasonable given the information you had at the time. You are not required to consider that something isn't what it appears to be. If a mugger sticks a gun in your face, that it might be defective or unloaded or he wouldn't shoot is irrelevant.