Most civilized people, the world over, do not sanction the murder of another human being. However, as in many things, there are exceptions as to whether or not the taking of another human being's life is duly classified as murder, depending upon, for instance, whether it was accidental, premeditated, in the line of defense, and so on and so forth. The very biggest dividing line, though, between that which is classified as murder and that which is not, often comes down to whether that taking of another human being's life has been officially sanctioned by the state, such as is done in wars or those engagements that are basically defined as war; as compared to an individual or a group of individuals, that take the life of another, just as deliberately, but have not done so under authorized state sanctioned circumstances.
That is to say, under the conditions of war, the taking of another human being's life can be something in which the killer of that person or persons is rewarded with a medal from the state, for performing their duty to that state. Whereas, on the other hand, those that take the lives of another on a non-state sanctioned level, of which they have no expressed or even implied authorization to do so from those that are the authority figures of that state, are never rewarded with a medal, and are typically seen as a true menace to society and hence are prosecuted by the state with the objective to have them incarcerated for their inhuman actions.
Yet, as much as states wish to differentiate between those that kill as authorized by the state, as compared to those that kill, without such authorization, the difference in the mindset of those that are doing the killing, may not be appreciably different, because in order to take the life of another, or lots of others, there often is a commonality in which the person or persons, that is the enemy target, has been effectively dehumanized, beforehand. In other words, to convince a soldier to kill the enemy, typically necessitates demonizing the enemy and dehumanizing the enemy by defining that enemy in derogatory terms that effectively takes away their semblance of humanity and replaces such with what makes them appear as something of no more importance than a despised animal or an insentient object. So too, street thugs of all types, look upon the other, not as a human being, but simply as a target that has to eradicated, eliminated, and silenced, in order for that perpetrator to get their proper respect, or money, or its equivalency.
To kill another person is not a natural act, which is why many that do so, have to take substances to gather the "courage" to do so, or are inclined to use such substances after doing so, in order to quiet and to still their mind. However, all this killing is always a lot easier, if the state, or the respect of the street, is able to effectively make it appear that certain particular human beings aren't really human, but are instead actually some sort of despised subspecies, that is a pestilence or an ever present danger that must be stopped at all costs.
While the killing as sanctioned by the state is dealt with in a fundamentally different manner than killing that has not been sanctioned by the state, what most pundits do not readily realize, is that the psyche of those doing the killing is uncomfortably similar in both of these respective actions, in form and in substance.