It's always tempting when we hear of a particularly horrendous crime to assume that the perpetrator must have "mental health issues". I believe that's because what has happened is so very far beyond our understanding, that we can't imagine that any "sane" person could possibly behave in that way. Unfortunately, criminal cases prove time and time again that there is more often than not no mental instability involved, as proven by expert, professionally qualified witnesses, and that the perpetrator simply has a criminal mindset, which facilitates behaviour which, in its most extreme form could simply be described as "evil". I'm not suggesting that this applies in this particular case, as I simply don't know enough about it. However, its relevance will certainly have been carefully and expertly considered as the case unfolded.