As I said, his personality seemed to completely lack any facet that would have rendered him capable of taking another persons life, which is what was so suprising, but then I only knew him when he was an old man..."
You're judging him by a higher standard than the 3 Germans, (who, by the way, were trying to kill him).
At times, a brave man does what he is forced to do...he didn't choose this situation, but rose to the task..and I might add that, because of men with this kind of character,
you are free to subtly disparage his.