The salient and significant factor here is police incompetence.
A highly unusual and complex case was inherited by officers with little or no experience.
Bodies everywhere (all a family/25 shots), and an overriding desire to have it all wrapped up quickly.
Essex police wanted to rival the Met on competence - ignoring details, and failing to make logical decisions.
CSI (an American series, showing how forensic analysis should be carried out) would have come up with a very different outcome.
Blood spatter and timeline factors would have been paramount.
Guilty or not - Bamber's case was handled extremely badly.
Most will agree with that, at least, when the series concludes.
Officers concerned will be incomunacdo - as they were soon after the horrendous events....