A crystal clear example of Fuzzy Fuji Logic.
None of which logic you dispute, correct? Because if you had a point to make you would have made it.
The point of bringing up Semrau was to demonstrate, via a reasonably current issue with which we're all familiar, that when a host country brings a war crimes trial against one of its own wayward soldiers it brings a murder trial. The charge is murder. Now Semrau was not guilty of murder, but what I'm point out to you is that murder is the charge that is brought, not some other fancy war crimes charge--it's a regular plain old murder trial.
They only time you get into fancy international courts prosecuting anybody for war crimes is when the host country won't or can't prosecute them itself. Then you get into some stranger laws with all sorts of interesting jurisdiction and fairly high standards to meet.
But a garden variety war crime ordinarily should be prosecuted by the host government using its ordinary courts and ordinary laws. Murder, attempted murder, etc., are already crimes in every country on this planet, it's just a matter of whether or not the government has a will to apply its own existing laws.