The problems appeared to have started after the father left to start a new home in Livingston.
"Born in July 1988, his parents Corinne and Philip split up when he was 11. He grew up under the care of his mother and she allowed him to do exactly as he pleased. He lived in a state of near squalor; keeping his own urine in bottles in his bedroom, rarely washing and wearing the same clothes for days on end.
Left largely to his own devices he became defiant, violent and brooding with an unhealthy fascination with knives, the occult and drugs. He was first brought to the attention of the mental health profession aged just 11, following a fight at King’s Park Primary in Dalkeith. Although the incident was just a minor skirmish with another pupil, Mitchell’s attitude was sufficiently troublesome to warrant a referral to a school psychiatrist. However, there appears to have been little further action taken by the education authorities or his parents to curb his behaviour."
http://www.scotsman.com/news/natural-born-killer-1-1401861