One thing to remember on the legal side is that self-defense is not such a low bar, but rather a high bar.
One consideration will be GZ's fear for his life. Was this fear rational?
Another consideration will be GZ's actions leading up to the confrontation. To what extent did he create the situation that caused him to fear for his life?
I don't know that his self-defense claims will be all that easy to support. That does not mean that it's impossible however.
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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."