This is one incident that we don’t have all the information about. You really going to sell out an entire country over one incident that isn’t immediately rectified during wartime where they have far more to worry about than prosecuting every crime immediately or else?
It sounds to me like the German Medic witness was working on someone else and caught the event out of the corner of their eye while busy. Otherwise, why weren’t they working on the prisoner (and hence in the way). So, the witness didn’t know the severity of the wounds, in an area that was low on med supplies (looking for bandages, with a medic in LOS?) and just assumed it was a hate motivated execution when it could just as well have been a mercy.
Edit: and this supposedly happened almost a year ago? How is this even news?