My take on this case is provisionally pro-guilt. 'Provisionally' because there is a lot of material I haven't seen. I would particularly like to read transcripts of Bamber's and Mugford's trial evidence and to see a complete and reliably-sourced set of the crime scene photos.
My principal reasons for favouring guilt are Mugford's evidence, which I see as credible, even though she had ample reason to lie, the unexplained delay in calling the police and the failure to call 999. Mugford makes better sense if she was involved in the murders as an accomplice. That reconciles the peculiar duality of her behaviour and her account. For instance, the temazapam story in which, knowing why he wanted to test it on himself she allowed him to do so. In my opinion, she very likely sourced the temazapam specifically at his request but slightly modified the story for the benefit of the cops.
Likewise, the phone call to her at whatever time it was on the morning on 07 Aug is likely to have been a ruse to provide him with some kind of alibi. Her account of it makes no sense at all. She says he said, 'there is something wrong at the farm, everything is going well'. The first part of that is likely what they agreed she would say he said, something ambiguous to give the impression he had not received a clear and distinct message from Neville. Since he had told her earlier 'tonight's the night' 'something wrong at the farm' would mean the plan had backfired or failed in some way, not that an unexpected emergency had arisen there.
Her involvement also better explains her hesitancy in coming forward. She took an enormous gamble in doing that. The police might have decided to go after her too or she might have faced liability for malicious prosecution. I don't think being jilted was enough to explain her actions.
Anyway, if she made up her account, she sure did a bad job of keeping herself out of it. Even taken at face value she was admitting very serious offences involving concealment and assistance following the crime. It is remarkable that she was not prosecuted for those but, maybe not, as it was in nobody's interests to pursue the question of her involvement - not Bamber's and not the cops'.
Whether Bamber received a fair trial is a separate and important question on which I have not formed a strong opinion due to not reading enough about it. I've read the 2002 appeal which describes and then dismisses a litany of errors and inadequacies in the conduct of the case. There are substantial concerns about the provenance of 'the' moderator, the state of Sheila's body when found and so on. It beggars belief that the scene was cleared of blood stained carpet and wallpaper the next day and the cretinous fumbling of Essex police, even to the extent of being unable to write down the time correctly, is truly staggering.
Nonetheless, through all that fog of blundering incompetence and perhaps worse, the theory that seems to fit best is that he did it with her knowledge and assistance as far as the alibi is concerned. That's where I am with this one.
