He used the Nuremberg defense to explain why he followed the illegal order.
Nuremberg defense
idiomAn explanation offered as an excuse for behaving in a criminal or wrongful manner, claiming that one acted in this way because one was ordered by others (particularly superiors) to do so.
Origin
disputed originAn allusion to a defense used by former Nazi officials prosecuted during the Nuremberg trials after World War II. The trials were held in Nuremberg in Bavaria, Germany.
During the trial, the soldier attempted to use the Nuremberg defense, arguing that he was merely following instructions from his commanding officer.
The lawyer rejected the defendant's reliance on the Nuremberg defense, asserting that personal moral responsibility cannot be surrendered simply because one is acting under the command of a superior.