We know JM claims in her WS that Bamber told her he was involved. This is not evidence he was involved.
The conviction hangs on one crucial piece of so-called evidence: a blood flake measuring around 1/4". Nothing more and nothing less.
There is plenty of other evidence, for example:
* evidence that Bamber called Mugford around 3am, 10 minutes before the supposed call from Nevill.
* neither Nevill nor Jeremy called 999
* Jeremy's hatred of his family and talking about killing them
* sheer lack of forensic evidence to suggest it was Sheila (no blood on her hand or feet, no gun residue on her hands, finger nails completely intact, etc)
* Sheila had no knowledge of guns
* The murderer over-powered Nevill, which suggests it was Jeremy rather than Sheila