As DD says, when there is no doubt whatsoever (such as filming the f*cking thing) and when it's crimes against children, acts of terrorism or serial killers. Huntley should have hung for example.
Any cold blooded murder should also be considered. It shouldn't be on the say so of one judge either, after conviction it should go to three judges, after the first judge has made his decision, as they do in the court of appeal. Barristers can then argue it out with the three judges.