I'm a little surprised to see that a great many people are willing to equate choosing not to act in someone's favor with specifically acting to end their life. I'll make no argument that watching someone die when you have the opportunity to save them isn't a callous, immoral act, but the two examples are very different. I'm no lawyer, but it was my understanding that Murder in the U.S. is split into three different classes. Murder 1 is premeditated. Murder 2 is committed in the heat of the moment, as it were. (The proverbial, crime of passion.) Murder 3 is depraved indifference. As I understand it, the test for that is, would any reasonable person have acted to save that person's life.
The operative distinction for Murder is Mens Rea. Your intent - your thought process has everything to do with the situation. So I suppose, two different players could make the same decision, and for one of them it would be murder (3) and for another it would be nothing at all, depending on the motivation behind the decision.
If a small act will save someone's life, and you refuse to do it, you are guilty of something. But, if that person is a traitor - if that person has willfully put you or others in mortal danger, you are under no obligation to help them, knowing full well that they may put you in mortal danger again. Bear in mind, that there is an in universe war going on. Providing humanitarian first aid to an enemy is the right (light side) thing to do, but not giving aid to an enemy is not equivalent to murder. (Unless they have surrendered to you, in which case, it's pretty awful.) Just the way I see it. Again, I'm no lawyer.