Sorry, the industrial frame would have been made on an innocent Bamber.
A guilty Bamber, the industrial frame is not needed.
Relatives find the silencer. Realising that Sheila could not or would not have used it, they plant blood inside inside it to incriminate JB.
Relatives report silencer to the police.
Police give silencer to lab.
Lab look at silencer un-aware of the circumstances it came it into being and conclude Sheila was murdered.
Done. Nothing industrial about it.