Once-is-one-time-too-many-byrnes

This is the 61st book in the long line of stories covering the life and times of Detective Grade Four Joseph Lind and his many partners.

It is alleged that there have been over 300 unsolved homicide murders in New South Wales since records have been kept. Slowly, there are examples of a number of these unsolved homicide murders being resolved, with the perpetrator being charged many years after the fact. With a different investigative direction and huge leaps and bounds in DNA trace examination, the villain is being charged—in some cases, forty years after the fact.

What makes these perps commit the crime of kidnapping a young adolescent or pre-adolescent female to commit horrendous acts before killing the victim, with the sadistic act never repeated? 

What giant inner forces were at work to commit these crimes? Never repeat a homicide murder on another pre-adolescent youth.

Most countries have examples of serial killers, but these are far and few between, with these ‘one-off’ acts being the norm. Why do these ‘animals’ cease their sordid behaviour, living in anyone’s neighbourhood and known to be quiet and unassuming fellows? Do these people have reoccurring nightmares, or is that past act exorcised from their consciousness?

What makes a serial killer continue while these other sadistic men stop at just one when once is too many for them?