Will We ever find a motive?

No one will truly know what drove Blackwell to murder his parents but, thanks to his case, Narcissistic Personality Disorder is now considered under British law to be a serious mitigating circumstance in murder cases.
Little is known about NPD. Psychiatrists do not know what causes it and have very little idea of how to treat it. All they can really do is diagnose it.
Blackwell had no evidence of a troubled background, which confused most people trying to find motives for his heinous and seemingly unprovoked actions. For the most part, there was an overwhelming sense of sadness felt for the entire Blackwell family and their dismal fate.