A loose translation of Torat Hamelech by Rabbi Yitzchak Shpira and Rabbi Yosef Elitzur of Yeshivat Od Yosef Chai

Chapter One

The Prohibition of Killing a Non-Jew

In 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-Jews
One 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 God, 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 killed
The 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 God it's written that killing a non-Jew is not considered a transgression of the commandment "Do Not Murder" at all. And so, theMinchat 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 prohibition
From 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.

Point 3. The Punishment
The Rambam writes in Chapter 2 of the Laws For One Who Murders:

One who kills a Jew or kills the slave of a Jew is then given the death penalty...[11] A Jew who kills a righteous non-Jew is not given the death penalty from the court, as it is written, "if a man plots against his fellow," and it is not needed to say that he will be given the death penalty because he killed a non-Jew. And one who kills another's slave (not Jewish) or kills his own slave(not Jewish) is given the death penalty because the slave has accepted upon himself certain commandments and is added to God's portion
That is, that a Jew who kills a non-Jew, even a righteous non-Jew, does not get the death penalty from the court. A righteous non-Jew is one who accepts upon himself the authority of the Jewish court to enforce the Seven Laws of Noah, and he is thus considered a part of the "righteous nations of the world". Similar to what the Rambam wrote in the Laws of Forbidden Acts During Marital Relations (14,7):
Who is considered a righteous non-Jew? One who accepts upon himself not to practice idolatry as well as an acceptance of the other Laws of Noah... Then, he is accepted as righteous and as a part of the righteous nations of the world...
A Jew who kills even a righteous non-Jew doesn't get the death penalty at the hands of the court or any other person, and the Rambam emphasizes the difference between a righteous non-Jew and a non-Jewish slave who belongs to a Jew. A non-Jewish slave who belongs to a Jew is a non-Jew who was purchased to be a slave for Jews, and he is in the process of becoming a convert. As a slave he is obligated in all the commandments incumbent upon a woman; and so he is "added to God's portion". None of these things apply to a righteous non-Jew.

In any case, the Rambam only speaks about the punishment here, and it is absolutely forbidden to kill a righteous non-Jew! And, it's not just forbidden to kill him, but a Jew has an obligation to help sustain him! And the words of the Ramabam are exactly such that "one who does kill a righteous non-Jew is not given the death penalty through the court"- meaning that it's still forbidden. The Kesef Mishna says rather that the punishment is from Heaven:
And our master wrote that he is not killed by the court, rather he is killed at the hands of Heaven (for killing a righteous non-Jew)
Point 4. The Words of the Rambam in The Laws of Idolatry
The Rambam writes in the Laws of Idolatry, Chapter 10:
[1]We do not end relations with idolaters, because we want to maintain peace with them, and let them continue their idolatry, as it says, "Do not end pacts with them". However, they must end their idolatry or they will be killed. In addition, it's forbidden to have mercy on them, as it says, "do not deal kindly with them". Therefore, if one sees an idolatrous non-Jew who is lost or drowning in a river one should not take him out. If one sees that he may die he should not be saved. But, it is forbidden to lead him astray or push him into a pit, that is if he is not waging war with us.
[2]From here one learns that it is forbidden to provide medical care for one who engages in idolatry even for the payment [of care] ... whereas for a righteous non-Jew, it is a commandment to help him and provide medical care for free.
From here we can derive three levels, or types of non-Jews:

A. A Righteous non-Jew: it is a commandment to sustain him, and is certainly forbidden to kill him.
B. A non-Jew who is not at war with us: It is forbidden to save him, and it is forbidden to kill him.
C. A non-Jew who is at war with us.

For a "righteous non-Jew" a Jew is commanded to sustain him - as the Rambam writes in the second law. And, so we have a clear source that forbids killing the righteous non-Jew. But, it is necessary to clarify the prohibition of killing a non-Jew who is not "righteous".

Point 5. The Limitations of the Prohibition
It says in the Mechilta on the verse Exodus 21:14:
"And when a man plans to kill his neighbor through deviousness, [the murderer] you will take him from my Altar to die" - A neighbor, meaning 'others'. Isi ben Akiva says that before the reception of the Torah we were warned about murdering another. And, after the reception of the Torah these restrictions were lessened. In truth, we became exempt from the laws of life and death. (Not to mean that we were permitted to kill. Rather, this is simply a way of interpreting this verse for the sake of exegesis)
It can be understood namely that from the word "neighbor" or "other" we learn that the killing of a non-Jew does not warrant the death penalty. Then, the words of Isi ben Akiva present us with two contrasting states - the state of "before the reception of the Torah" where we were bound within the confines of the laws given to the offspring of Noah - and the state of "after the reception of the Torah". The Marchevet HaMishna comments on the words of the Mechilta:
"And, after the reception of the Torah these restrictions were lessened? - That's a surprise!"
That is, can we say that it's possible that once the Holy One Blessed is He gave us the Torah and all is commandments, which included commandments that were previously given to us, suddenly that which was previously prohibited (such as killing a non-Jew) is now permitted? Thus, in our own time was are warned about killing a non-Jew (it is prohibited).

According to this the continuation of the Mechilta "In truth, we became exempt..." is understood: Although it is forbidden for a Jew to kill a non-Jew just as a non-Jew is forbidden to kill a non-Jew - just as it was before the reception of the Torah - there is a slight change for the case of a Jew killing a non-Jew: A non-Jew is given the death penalty for killing another non-Jew, but a Jew isn't given the death penalty by the court[for killing a non-Jew]. This is because after the reception of the Torah a Jew is already obligated to follow the 613 commandments in the Torah, and the killing of someone who is bound by the 613 commandments- this has to be an act that warrants a punishment with a special stringency. The source found for the Seven Commandments given to the Offspring of Noah and their accompanying punishments don't suffice. And therefore when a Jew kills a non-Jew he is not given the death penalty by the court. Rather, the Jew is killed at the "hands of Heaven."

Furthermore, we learn from the words of Isi ben Akiva in Mechilta that the prohibition of a Jew killing a non-Jew is in virtue of the prohibition of killing given to the offspring of Noah. Jews are also included in this prohibition. However, we were given a special addition to this prohibition, "Do Not Murder", which relates only to the killing of a Jew. And thus, a few warrant the death penalty.

Point 6. There is nothing permitted to a Jew that is also prohibited to a non-Jew
This principle, that Jews are bound by the Seven Noahide Laws - is also found in the Talmud, Sanhedrin 59a:
There is nothing permitted to an Israelite yet forbidden to a non-Jew.
And this is exactly what is said in the Mechilta,
"And, after the reception of the Torah these restrictions were lessened? - That's a surprise!"
The Rambam emphasizes this principle, that a Jew is definitely obligated in the Seven Noahide laws. He says this on the point about the seven commandments (the beginning of Laws of the Kings, chapter 9):
Six precepts were commanded to Adam:

a) the prohibition against worship of false gods;

b) the prohibition against cursing God;

c) the prohibition against murder;

d) the prohibition against incest and adultery;

e) the prohibition against theft;

f) the command to establish laws and courts of justice.

Even though we have received all of these commands from Moses and, furthermore, they are concepts which intellect itself tends to accept, it appears from the Torah's words that Adam was commanded concerning them.
The prohibition against eating flesh from a living animal was added for Noah, as Genesis 9:4 states: 'Nevertheless, you may not eat flesh with its life, which is its blood.' Thus there are seven mitzvot.
These matters remained the same throughout the world until Abraham. When Abraham arose, in addition to these, he was commanded regarding circumcision. He also ordained the morning prayers.
Isaac separated tithes and ordained an additional prayer service before sunset. Jacob added the prohibition against eating the sciatic nerve. He also ordained the evening prayers. In Egypt, Amram was commanded regarding other mitzvot. Ultimately, Moses came and the Torah was completed by him.
One can say that the Seven Noahide Laws are the beginning of the Torah, and Moshe completed it through the reception of the Torah. And even though the laws might be nullified after the reception of the Torah, we were bound by them before. If so, just as before the reception of the Torah we were prohibited to kill a non-Jew, so to are we prohibited from killing a non-Jew after the reception of the Torah.

Point 7. Additional Considerations
Aside from the biblical prohibition of killing a non-Jew because of the prohibition of 'spilling the blood of another person'- it's appropriate to mention the words of the Sages in Tanna Divei Eliyahu on the stringency of killing a non-Jew. [One should not kill a non-Jew] because it is a desecration of God's name, and the fate of a person who kills a non-Jew is that ultimately he will kill a Jew.
...The end of one who kills a non-Jew is that he will kill a Jew. All of this is ultimately done to sanctify His Great Name.
From this a number of obligatory laws can be extracted. One should not even harm a non-Jew (even those who desecrate the Seven Laws of Noah, simply because they deserve the death penalty, which will be clarified in chapter 2) in order to prevent a desecration of God's name. These laws are stated in order to prevent loathing and for the sake of peace (between Jews and non-Jews). And, certainly in matters that pertain to 'killing a non-Jew', one must consider if such grounds are even realistic (the era, country of residence, etc).

Point 8. Summary

1. It is forbidden for a non-Jew to kill another person. And, if he does he is sentenced to death by the court.

2. The prohibition of "Do Not Murder" (as found in the Torah) is related solely to a Jew who kills another Jew.

3. A Jew who kills a non-Jew is not sentences to death by the court (by Heaven though, this is a different matter...).

4. One can derive from the prohibition of a Jew killing a non-Jew that it is prohibited for a non-Jew to kill another non-Jew, as it says in the verse "spilling the blood of another person"; meaning that "what's prohibited to a non-Jew is never permissible to a Jew".