I don't think that it's really comparable. If we believe his story, we know that he fired his weapon recklessly without checking his target first. If you were to compare it to a driving offence, I guess the closest would be causing death by dangerous driving.
Only if you apply the scenario here.
He's not here, and therefore that is, IMO, the best match.
If he truly felt that his life was in danger then his actions are explainable and that is entirely relevant.