For most of us, a violent crime is shocking enough on its own. The idea that someone can cross every threshold of decency and attack another person to the point where they lose their life never stops being difficult to accept.
Yet if nothing else, in many cases we at least have some understanding as to what drove a murderer to do what they did.
And so, cases where even the reason for the act is a mystery become all the more chilling. Although the case we're examining today has been going on for three years, we're no closer to understanding why it happened.