DNA: Kolkata Rape -- Conspiracy to prove the rapist to be mentally ill?

There is outrage in Bengal against the murder of a lady doctor after her rape inside the hospital. It is being said that more than one person was involved in the rape-murder. Amidst all this, it was being said about the accused Sanjay Roy that he was mentally ill and due to his mental condition, he raped and murdered the lady doctor in such a gruesome manner.