The relatives would need to know -
Is Bamber innocent.
Sheila's arm lenght.
The rifle lenght with silencer.
Could Sheila have shot herself with the silencer attached.
What back splatter is.
Who of the 5 deceased received contact shots.
What locations would contact shots need to be to produce back splatter.
Where were the contact shots on the 5 deceased.
Is there any other forensic evidence against Sheila.
Was there a silencer next to Sheila.
How to realistically put blood into a silencer.
Where was Sheila's blood to insert into a silencer.
Did the rifle barrell already have blood on/in.
Did the crime scene photos show an unscratched aga.
Had the police already checked all silencers at WHF.
The chance of this one piece of framed evidence getting a conviction.
The punishment if caught doing this.
Confidence in each other that none would succumb to police pressure.
Sheila's blood group.
The blood group of each other.
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This had to be found out very quickly. Providing they have the idea & decide to go ahead.
"The Gish Gallop is the fallacious debate tactic of drowning your opponent in a flood of individually-weak arguments in order to prevent rebuttal of the whole argument collection without great effort. The Gish Gallop is a belt-fed version of the on the spot fallacy, as it's unreasonable for anyone to have a well-composed answer immediately available to every argument present in the Gallop. The Gish Gallop is named after creationist Duane Gish, who often abused it.
Gish Gallops are almost always performed with numerous other logical fallacies baked in. The myriad of component arguments constituting the Gallop may typically intersperse a few perfectly uncontroversial claims — the basic validity of which are intended to lend undue credence to the Gallop at large — with a devious hodgepodge of half-truths, outright lies, red herrings and straw men — which, if not rebutted as the fallacies they are, pile up into egregious problems for the refuter."
http://rationalwiki.org/wiki/Gish_Gallop