[int_19h]

Not quite. If the Allies prosecuted German pilots and their commanders for, say, strategic bombing of London - including civilian targets - then yes, it would have been a sham. But they weren't, precisely because the Allies did it too. So the atrocities people were prosecuted for at Nuremberg was stuff like shooting surrendered prisoners, or deliberately executing civilians in controlled areas.

[turar]

Yes. However, I was merely applying gizmo686's criterion of a crime, "it has to be a standard that was at force at the time of the attack", to Nazis in similar fashion as (s)he applied it to Allies.

And Nuremberg trials was famous for doing precisely what gizmo686 described -- charging defendants with "crimes" that were defined as crimes after the fact. https://en.wikipedia.org/wiki/Nuremberg_trials#Criticism

[int_19h]

The way they did it was by claiming that the crimes didn't stem from any written law, but rather from an unwritten universal (for Europe, at least) custom. This is not actually all that far fetched - the notion of "customs of war" long predated any formal conventions etc.