Comment: At the moment he chose to pull the trigger, there was -- literally -- no threat, no possibility for "any degree of force" to be used against anyone. 

These aren't just facts - they're uncontradicted facts. The defense is just hoping the jury will ignore the facts by (a) convolution of the time frame so that earlier events are intermixed with later events, (b) pointing to facts unknown and unknowable to the defendant at the time, and (c) insisting that possibilities that are physically impossible could be possible.

That said, I'd be betting on juror nullification of the law in this case. 

But kudos to the prosecutor for not ignoring such a clear-cut, textbook case of cold blooded murder - in El Paso Cty nonetheless! (That fact alone should convince observers of how obvious a crime this was. Prosecuting a Green Beret for executing a scumbag! I'm certain the prosecutor looked for any alternative other than prosecution! Now that is dedication to the law - lady justice with a blindfold.)