I don't remember the original case at all and had actually picked up the story via an Australian newspaper!
Only saw the last night one, but enjoyed it.
We have all got used to the speedy cases in Midsummer Murders etc when police tramp all over the evidence and it's all sorted within an hour so this would seem slow. But especially with cold cases , according to a policeman friend of mine, that is how it is, like putting together a jigsaw.
Sorry, but couldn't see the excellent Luke Evans without thinking "Beauty and the Beast"!!