Atrocities like this happened on a much more grander scales than the single life of a lone sniper, many civilians and alike were not even afforded an opportunity to surrender and were brutally murdered for nothing, the countless bombings of civilian towns on both sides was terrible enough.
War is beyond anyones comprehension and certainly morality takes a back seat to survivability, its either kill or be killed.
These types of things happened on all sides of the war, some more than others, too many of these types of stories are out there, Japan was one of the worst culprits of the time.