Like Dotsie says the presence of DNA evidence isn't always 100% conclusive so police must still prove the crime within reasonable doubt via the usual methods of putting the perpetrator at the crime scene with established motivation and other types of corroboration such as CCTV footage, witnesses etc. Even in rape cases (and lets leave sexual politics out it for a moment) where it's a 'regular' relationship by date or cohabitation the police still have a job to nail things, especially if there's no definitive physical evidence of a struggle to show that force was used in some manner...
And then there's the Derek Bentley argument... (the 'let him have it' case where the gunman was 16 and the educationally-challenged but adult Bentley was his partner in the interrupted robbery where a copper was killed) where the evidence is suspect or just plain mistaken. At least if someone's jailed then they have the appeal process which is by no means a pushover, but at least means those few people who are wrongly imprisoned have a chance to prove it eventually.
I personally believe that life imprisonment (and I mean life, not 20 years or whatever with parole) is a better punishment for really hard core crimes where a life has been violently ended or irretrievably ruined (so rape etc) as then the perpetrator has their life taken from them and must suffer for it to the end - just like their victims or the families and friends whose lives are likewise blighted. In cases like the Moors Murderers, human rights arguments should rightly have no effect because there's no reprieve for people like the mother of Keith Bennett who died recently without his body ever having been found so she could at least know he had a decent burial. That's a far better Justice system whether or not the prisoner has been rehabilitated. Why should they have their life back no matter how sorry they are or how little is left of a sentence?
I think that's actually a far better deterrent and more civilised alternative to execution where animals like this man are forced to live with the consequences of their actions for the rest of their miserable days.
I hope they throw the book at him and anybody who harboured him while he was breaking bail. Prison's also more of a deterrent I think - there's no glory hole then for psychos like this guy.