Would it be safe to say that anyone who murders someone, commits a heinous act or is considered 'evil' suffers from some sort of mental illness of varying degree.......?
I can never correlate the difference.
I always find it interesting however the different reactions of when a filicide is committed.Take for instance the Port Lincoln murder/suicide. The Dad that killed his 2 children. The social media and msm commentary on that as per my observations seemed to consist mainly of empathy towards the Father with calls for better metal health services even though it was acknowledged by the family that he had been encouraged to seek some help but refused. He was heralded as a 'good bloke' and many other wonderful things. From what I read most people were sympathetic towards him. I wonder if this is because he killed himself too?
Father's generally kill their children as an act of violence towards the mother and is about control and revenge, for Mother's it seems to be more about feelings of hopelessness and a perceived lack of support however that is mainly in the context of filicide/suicide.
Anyway just my observations and thoughts.
Here is a link to a very good study on filicide in the context of separation.
http://www.dvrcv.org.au/sites/default/files/‘Just Say Goodbye’ (January 2013 online edition).pdf