We may be sure that many a serial killer lurked in the ranks of armies of old, using the chaos of war to cover their careers of rape and murder. Discipline within the ranks and the screening of recruits greatly reduces this in the armed forces of modern nation-states, but certainly a few still slip through. Guerrilla groups, insurgents, militias? The incidence of such individuals is bound to be higher.
The writer of fiction needs to recognize that men (primarily) of this sort exist. They are not the norm in the military. For better or worse, soldiers are like any other group of men. Some will be weak and do wrong, but they are not the sort of psychopaths of whom I am speaking.
One of the major characters in DONZALO’S DESTINY is — the sergeant of Lord Radal’s private guard turned mercenary captain, Sojel. A man who fled his home nation of Muradon and probably some other places, he lusts for pain and death.
He is not a sociopath, as we normally understand the word. Sojel values loyalty and is exceedingly loyal to (and fears) his dark master, the sorcerer Radal. He does not manipulate people. Perhaps he even empathizes with people, in his way. But he really, really likes to kill them.
By the way, we do introduce a sociopathic individual in the young diplomatic aide and fledgling wizard, Benawis, whose schemes exist solely for his own advancement. Let us just say that those schemes lead him elsewhere.
But to return to our original topic — there will be serial killers and psychopaths hiding among the men of any army. It would be an attractive life for many of them, a license to fulfill their desires with impunity. This is a fact if we deal with an earlier era, or a fantasy milieu that borrows from history. At the same time, we must take care not to paint all the military with that same brush, especially in a more modern setting.
Take care with the psychopath, with the mass murderer, the serial killer. He is not the ordinary criminal, the mundane brute who indulges his lusts when the opportunity arises. That individual, too, exists as soldier, as outlaw, as the ordinary-seeming fellow down the street. But he does not live for such things. They do not drive him.
This sort of thug is common and likely to pop up in any adventure-oriented tale. And, in his way, he may be more interesting to write about than the psychopath because he can be redeemed. He is not broken beyond repair. The serial killer almost certainly is.
One more thing I might say is not to attempt to delve too deeply into the minds of these people. It almost always comes off as facile pop-psychology and soon seems dated. This is true of many of the ‘psychological’ novels of a century or so ago. Better to simply present them, tell of what events formed them, but do not try to explain them — at least not in any detail.
Do recognize, however, that they exist and that they would, in the past, have frequently been attracted to the ranks of the military.