The convictions of those you refer to are not Afaik underpinned by witness testimony where the witnesses were given immunity against prosecution and/or some sort of personal gain/favourable treatment in exchange for the testimony unlike the following:
Michael Stone - Damian Daley
Michael Steel - Darren Nicholls
Jack Whomes - Darren Nicholls
Jeremy Bamber - Julie Mugford
The above all protest their innocence.
JB - 99.9% innocent imo
Steele/Whomes - 80/90% innocent imo
Stones - Don't know enough to put a % on it
Julie Mugford wasn’t given immunity on her one-off cheque book spending spree fraud she did one Saturday, on the proviso she owned up about what Jeremy had told her how he murdered his family...
She’d ALREADY volunteered the dreadful truth to the police before they they even knew about the cheque book spreading spree.
So you’re wrong.
Besides, even if Julie had been charged with her friend for falsely reporting her cheque book stolen and then going shopping using it, as she had no criminal convictions; owned up to it (she could have denied it); and paid the bank the money back — had she been charged she’d probably have been fined, given a conditional discharge, and that would have been the end of it.