Jackie was plaing on your own prejudices there. She wasn't admitting that Jeremy had committed the murders.
Yes I know, that's why I responded somewhat flippantly.
She was saying that if the relatives believed that Jeremy had committed the murders then why did they not act accordingly with Julie Mugford and make sure she was done as well for accessory after the fact. As far as I can see that is all Jackie is saying here.
I have no idea, I wasn't there.
But let's just, for the sake of discussion only, say that JM was telling the truth, she had asked JB several times after the murders if it was him, he said no.
So before and after the murders JM was not sure, she perhaps put JB's previous comments down to him being a bit fantastical, story telling.
Then afterwards she started having more doubts, not wanting to believe that the man she loved was capable of such an act she didn't act on her doubts.
As time passed the doubts increased, then others (them pesky, greedy good for nothing relatives) started to consider JB was responsible, the doubts increased further and she went to the police.
(Yes I know there's other bits in there about being jilted etc.)
If something like the above occurred, then perhaps the relatives would be grateful towards JM rather than going hammer and tongs to get her banged up as well. After all she was also the star witness and ultimately her statements were responsible in part for allowing EP to charge JB and then secure conviction against him. Something the relatives were clearly happy about as they were convinced he was responsible.
So why would they hate her?
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This isn't black and white and just because somebody doesn't think or act the way in which you would expect, it doesn't mean that the assumptions that you make and the conclusions you draw are the only realistic possibility.
Likewise you could apply that to JB and some of his actions, but that's why were all here discussing the case and going round in circles.