He killed someone who was going to to die anyway – don’t think I’ve seen anyone claim he was other than fatally wounded.
Should not have done it. Should not have made light of it. Should have been jailed for it, and has been. But not the same as the summary execution of an able bodied prisoner.
Very difficult to decide if the sentence is sufficient. I feel it probably is, in the specific circumstances of the case.
Is he subject to a dishonourable discharge as well, if these still exist?