I think that what Rosina meant was that if the crutch had come from a charity shop, which we know it didn’t, then it would have numerous fingerprints on it.
Also I imagine the police have plenty of real stuff to analyse, without doing extras to win a bet.
Oh, I know we don’t need to watch it, but the daft storylines…. the accident and crutch, Tim and his secret heart condition, the never ending traumas at Speed Dahl, Chesney proposing to bike to another job in the middle of the night…..