One thing for sure,they couldn't have been Jeremy's because we'd have all known about it long before now.
I have never been able to think of a reasonable explanation why EP would have framed Jeremy Bamber. However, have just had a thought come into my head .....
We know EP went with four murders and a suicide but some members of the force were never convinced and believed it was JB, over a short time those believing him guilty managed to convince doubters he was in fact guilty. At the same time the relatives were pressurising with the same opinion.
Taff was removed from the investigation and the case became five murders with Jeremy Bamber as the perpetrator. This caused an uproar in the media as EP were seen as incompetent idiots and Taff Jones a highly successful DCI was personally diminished etc.
What if, at some point after changing direction and the evidence of the moderator had been exposed there was a discovery which showed proof JB couldn't have carried out the murders or that Sheila did? Would EP have had the courage to say they had been wrong all along, Taff was right and Sheila did kill the family and commit suicide.
Most of EP force wouldn't need to know about such evidence it could have been disappeared by a few people and no one was ever the wiser? That would be a reason for EP to frame or not just tell 'the truth, the whole truth and nothing but the truth'
Just a thought and there may be a reason I haven't thought of why this isn't possible any ideas?