Murder is a word with a strong negative connotation. Murder refers to the premeditated killing of a person, and it is usually associated with cold and cruel feelings. In this excerpt, the speaker wants to make it clear that he believes offensive wars are never justified. His use of the loaded word "murder" highlights the illegality of it, while at the same time gives the reader a negative feeling.
It is probably murder, because the word is most commonly thought of as being hateful and full of unbridled emotion, and in this particular passage, it is most likely used to convey disgust.
