BS”D
Mored bemalchus? From an Old Yishuv perspective, the malchus were the Turks and then the British. His mission (which I do not believe was taken seriously by anyone except the paranoid Zionists) was one of pikuach nefesh in the minds of his sponsors, and was therefore construed as similar to that of Rabbi Yochanan ben Zakai’s contacts with the Roman emperor that resulted in the “kerem beYavne” (NOT to be confused with the present hesder yeshiva of that name!)
DeHaan was a strange character, and I believe he was chosen only because he spoke several European languages.
As such, his murder was pure rishus, the slaughter of a truly innocent individual who posed no credible threat to anyone. Hate to use secular references, but it was a clear case of “killing a mockingbird” (if you don’t get the reference Google it because I am not a secular lit teacher LOL).