If you can find it, please produce it. I’m a historian and I cannot ever recall seeing any such apology from either Germany or Japan.
They did apologize to the Jews.
I assumed it was common practice to execute soldiers who attempt to surrender, especially in long, drawn out wars. That everyone did it, even if not "legal." But I didn't have a link.
Then today I stumbled upon the "Baralong incident." Baralong Incidents.
Baralong sank U-27, which had been preparing to sink a nearby merchant ship, the Nicosian. About a dozen of the crewmen managed to escape the sinking submarine, and Lieutenant Godfrey Herbert, commanding officer of Baralong, ordered the surviving sailors to be summarily executed after they boarded the Nicosian.
All the survivors of U-27's sinking, including several who had reached the Nicosian, were shot by Baralong's crew.