According to the detective, Harrison was attacked by Mann after Harrison went to his prison to keep a watch while Mann and Parr engaged in a sexual activity. Perr then shut down the door and Mann attacked him with a pen which was pierced into Harrison's eye. Mann tried to cut off his head with a knife and then slit open Harrison's stomach.

Mann and Parr then informed the senior officer about the brutal killing. Mann had been convicted for killing 2 women in a nursing home Leicestershire nursing home while Parr was serving a sentence for attempted murder.