What an interesting story. I'm not sure how like the U.S. criminal justice is the British one, but, in the U.S., you would not be committed to a forensic psychiatric hospital unless you successfully pleaded not guilty by reason of insanity. And, if that was the case, you would be a patient (not an inmate) and your stay would be based on your mental stability and violence risk, not the amount of harm your original crime caused.