They hung themselves with their own embellishment. Sending those letters to themselves. Up until then I was sure they'd get off. Thoroughly unpleasant pair but not enough evidence to convict. (some of the evidence the prosecution and police introduced was farcical.)
Big up to the Scottish benefits system for paying out £180,000 to someone who disappeared in the last century. (and the SS for their care) If that new rule hadn't been introduced, the couple would, almost certainly, still be getting away with it.