I'm no lawyer, but it's probably so they can figure out how exactly to charge and sentence him. For example, my husband knows someone who was murdered a few years ago by her husband. Although he confessed tot he murder, his lawyer was trying to get the Crown to make a plea deal for manslaughter. The Crown wanted to prosecute for 1st degree murder. So they went to trial and let the jury decide; 1st degree or manslaughter? He was convicted of 1st degree murder and is going to die in jail (cuz he's 60 something)