It was impossible for the relatives to fabricate the silencer without police assistance. See below.
The police didn't need the relatives to fabricate the silencer.
However the other option is the police fabricated the silencer. Then asked the relatives to pretend they found it & committ forgery & perjury. This thread post shows this is too ridiculous to comtemplate.
So what happened ?
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They were law abiding citizens.
They would have to have the crazy idea in the first place.
If caught they could be put in prison.
If caught, a rich Bamber could sue.
If caught, a rich Bamber could be their enemy regarding farm and land business.
They had to agree together & ensure everyone's account matched.
If one relative cracked under pressure, everything falls apart.
The police & defence lawyers will put pressure on each relative regarding their accounts.
None of them had attempted anything like this before.
They were already wealthy.
They did not know whether other evidence showed Bamber was innocent.
Taff Jones was not co operating with them & would have had a negative reaction to the silencer.
A fabrication attempt was a 1 in a million shot.
They may not know about human back splatter.
They did not know Sheila's blood type.
They did not know Sheila's arm lenght.
They did not know if Sheila received a contact shot.
They did not know if the rifle nozzle already had back splatter.
They would assume the rifle nozzle already had back splatter on as 25 shots had been fired into 5 people from close range.
They did not know how to correctly put blood into the silencer baffles.
They did not know how to scratch the aga to replicate a kitchen fight.
They did not know if crime scene photos already showed the aga without scratches on.
They did not know if the police had already checked the silencers at WHF for blood.
The fabrication was a huge life term committment. Creating false WS's & perjury.
Even if successful with the fabrication, it may not result in a conviction.
Bamber had already said he left the rifle at WHF without the silencer on.
It is possible Bamber would go out to shoot rabbits without a silencer attached.
They did not have time to plan & execute this as quickly as they did.
If the fabrication attempt failed & became public knowledge, they would be labelled as callous criminals throughout the nation & local community.
They were relying on one piece of false evidence to try to convict a perhaps innocent man of killing 5 members of his family.