GZ had to be able to reach even faster for the gun in that case. As he used it.
The jury will be asked to decide if his use of the gun was reasonable in the situation. What other options did he have?
Let's see...
toss the gun aside
fire the gun as a warning
secure the gun away from Martin's grasp.
I don't know that GZ's fear for his life was reasonable even if Martin reached for his gun. But that will take some extensive argument on both sides to determine. And different juries will likely reach different conclusions.
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justitia omnibus
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"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so."