I can't believe this but I just found out that the 'controversial' manuscript for Torah HaMelech (Torah of the King) is available on the web...
http://torathamelech.blogspot.com/It seems only Chapter One is available at this time..
Chapter One: The Prohibition of Killing a Non-JewIn this chapter we deal with the notion that the prohibition of 'don't murder' doesn't apply in the context of a non-Jew. And, the prohibition of Jews killing non-Jews is learned from the prohibition given to the offspring of Noah against killing others. In the appendixes of the chapter we deal with another principle that the Jews are obligated in the commandments given to Noah.Point 1. Shedding Blood Amongst Non-JewsOne of the seven commandments given to the offspring of Noah is the prohibition against shedding blood. In chapter 9 of the Laws for a King the Rambam says:
[1]Adam was commanded six things: not to engage in idolatry, praising G-d, no shedding blood, no immodesty, no theft, and establishing a court... another commandment was added for Noah, and that is not eating the limb of a live animal... [10] a non-Jew that kills another person, even a fetus in his mother, he will be killedThe words of the Rambam deal with a non-Jew who kills a non-Jew. So, here we will clarify the law that deals with a Jew who kills a non-Jew. Is such an act forbidden, and if so what is the extent of the prohibition?
Point 2. "Do Not Murder"
The Rambam wrote in chapter 1, law 1 of the Laws of Murder
Anyone who kills a Jew transgresses a negative commandment, as it says, "Do not murder". And, if he did it with malice in front of witnesses he is killed with the sword.The commentary here suggests that the prohibition of "Do Not Murder" related only between Jews, and not for a Jew who kills a non-Jew even if the non-Jew is from one of the righteous nations of the world. Also, in the book Fearers of G-d it's written that killing a non-Jew is not considered a transgression of the commandment "Do Not Murder" at all. And so, the Minchat Chinuch wrote:
One should not kill a single person, as it says, "Do not murder"-...but the killing of a non-Jew and even a righteous inhabitant of the Land of Israel that has accepted upon himself the Seven Commandments of Noah's Offspring are not included in this prohibitionFrom what we currently have in our hands and understand about the verse "Do Not Murder" it's impossible to learn the prohibition of killing a non-Jew.