I'm not completely convinced that religious fanaticism = mental illness.
Why not both? What if the family of this shooter produced doctor reports, prescriptions, psychiatric notes about his paranoia and delusions, would you then allow that maybe he had mental issues, as well as being Muslim and fanatical?
Also, when you see people on the street wearing sandwich signs proclaiming God's Kingdom is nigh and calling on passers-by to repent, do you assume that their religious fanaticism means they are mentally sound? Or do you think that part of their illness is the fanaticism?
Its interesting to me the push to remove "mental illness" from this guy by the same people who were only too happy to apply it to Bissonet, even though the profiles of the two killers seems pretty similar at this point and remarkably similar to many of the school shooters in the US.