[Because sometimes military law is stupid? "Rules are rules" isn't a good defense for a stupid rule.
If the guy and his witnesses are telling the truth, I'd have a hard time convicting him of anything. The guy he put out of his misery had half his head blown of and was going to die anyway- his last minutes (or hours) were likely going to be spent in incredible pain, if he had the ability to process pain with half his brain gone.
If he wanted to be malicious, there's a lot worse things he could have done. Sounds like he choose to make the most compassionate decision he could at the time, and he didn't care about the consequences, because doing the right thing was more important to him.]
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Anti-"mercy killing" as I am, and though upon reflection I might change my mind, I do believe that in the same situation my reflexive humane impulse would be to end the man's hopeless suffering as quickly as possible.
And I see this as exactly that: the automatic reaction of a horrified & humane man in the heat of battle.
BUMP