No one, even a mental health professional would diagnose someone without meeting them, so none of us can say categorically whether he is or he isn’t.
Any declaration of certainty are to be considered cautiously - although something like ‘if he was the defence would have raised it’ is a weak argument; he wouldn’t have been the first defendant to get poor legal advice.
He himself may not have wanted it to be used as a defence initially so his whole defence ignored it. We won’t have any knowledge therefore of any diagnosis that was made prior to it.
Additionally he might not have consented to any MH assessments, so no diagnosis was able to be made accurately
As miuch as some people like the idea of not giving someone an excuse of mental illness or disorder, he might well have a mental illness or maybe more likely, a mental disorder such as psychopathy.
Ho horrendous a crime doesn’t dictate the likelihood either way of the perp have disorder or illness.
All we know is that he’s been considered mentally fit and found guilty. I’d love to have trust in the legal system to be sure his fitness is accurate, his advice is appropriate and the clamour to convict and the will to not be seen as ‘going soft’ hasn’t led to poor treatment of someone, if unwell, has been poorly served.