I recall reading:
There were two silencers. In fact, they are not silencers like the illegal ones you'd expect a hitman to use. They are sound modifiers (for hunting rabbits)
The first silencer was taken as part of the evidence by the police. The second was found by the cousin's family in the gun cupboard once they had access to the crime scene.
The two silencers merged into one in the minds of the jury.
The blood on the silencer handed in by the family was said to be either Sheila's, the Uncle's or belonging to rabbits.
There were flakes of red paint on the silencer matching scratch marks in the kitchen. These scratch marks were not present in the crime scene photos.
It's suggested that, believing JB to be guilty but looking like he might get away with it, the extended family decided to 'strengthen' the evidence on the silencer.