Maybe, but tell me what sane person would attack his roommate with a hammer? I am sick of the stigmatization of the mentally ill via acts like this that are committed by people who are clearly unbalanced (because, again, this is not the act of a sane man), but who through their unwillingness to accept responsibility for their actions feed into the public's fear that mental illness is a precursor or a cause of violence. My best friend during my high school years was diagnosed with schizophrenia at the age of 16 because he had begun having auditory hallucinations, but he was never violent. Incoherent or difficult to reach sometimes, yes, which is plenty scary on its own, but I am very wary of this rush to find a mental defect to explain away what this man or many others like him have done. The Colorado theater shooter comes to mind, and perhaps even the "Twinkie defense" of yore...methinks this is why there is a legal distinction to be made between someone who is mentally unbalanced to the point of not being able to form premeditation on the one hand (so I could see this man getting some kind of reduced sentence on the grounds of reduced mental capacity at the time of the act), and someone who is actually mentally incapable of distinguishing right from wrong (or else every serial killer or other sick person could claim such an exemption from punishment).
Bottom line: The guy himself does not say that his religion motivated the attack, but does want to mitigate what he did with claims about his mental state. Fine. Clearly, he is a sick man. That said, I hope they throw the book at him, or as much of the book as UK law allows.