I've always wondered if it's a matter of translation; namely did the the tablets brought down Mt. Sinai by Moses prohibit killing or murder? From what I can tell, most people think "Thou shalt not kill" fully covers the topic, generating reams of argument about - what else? - the Death Penalty. Whatever the translation problem, however, it's evident that death at the hands of another is a long-standing human problem, big enough to make the commandment list alongside coveting, which appears to be an even bigger problem since it filled three slots out-of-ten.
The difference between killing and murder is not simply a matter of nuance. Semantically, all murder is killing, but apparently not all killing is murder. The distinction appears as a matter of agency, which is to say killing is not murder if it is sanctioned by the state. It is this distinction which guides the conduct of most modern armies, law enforcement, and prison guards; in defending peace one who kills others is regarded as noble, and is placed in a position of honor. Accordingly, to be killed in the act of defending others, while following orders or as a matter of principle is called "the ultimate sacrifice" and we solemnly lower our heads in recognition at sacred ceremonies.
Death at the hands of another may indeed be a "sacrifice" in some cases, but it's sometimes purely a matter of perspective. Did Eric Garner make the ultimate sacrifice for a matter of principle when he died on a Staten Island sidewalk while suffering a policeman's choke-hold for selling loose cigarettes? Did the punishment fit the crime or should his name be honored in the Tobacco Hall of Fame as a fallen defender?
Armed forces recruiters never explicitly say "join us and get permission to kill" but it's an underlying sales pitch. Same could be said for police work and guarding prisoners; the job confers authority to exercise lethal power backed by the agency of The State. The controversy arises when circumstances indicate that "force" - as it's euphemistically called - is used inappropriately and without just cause. When and if this happens, "killing" becomes "murder." The dividing line's not exactly clear, which with coveting is why courtroom's were invented.
The Islamic State, for example, is against killing, except when it's done in the name of The State; it should be noted, however, that slavery and amputations are ok. What we might conventionally call murder ISIS calls killing, and the idea is so attractive to some that homicidal recruits from all over the world are flocking to ISIS to get in on a piece of the action. Cloaked in fundamentalist interpretations harkening back to medieval times, ISIS takes the words of the Koran strictly literal and the implication of a reestablished Caliphate seriously. Like any strictly literal fundamentalism, to many of us this sounds crazy, but then much of our Bible sounds crazy if taken literally.
Non-violence has also been used as a selling point, but regrettably, with far less recruiting success. It's one thing to die at the hands of another, but for most giving up the opportunity to kill in return lacks a certain element of reciprocal symmetry. So it appears we're stuck with our tragic and uncomfortable situation, fearing death while embracing it at the same time. Good for gun sales, bad for bodies.