The police indeed did burn evidence, but this was with the consent of the major presumed victim, Jeremy himself, and it was for a perfectly justifiable reason. What else were the police supposed to do? Open a gothic museum with it all? They acted properly in the context of Jeremy as an innocent party. When it became clear (in their eyes) that he wasn't so innocent, they quickly admitted their error and took steps to rectify matters and collect further evidence. If Jeremy is guilty, then you can't ask for more.
My considered view, having reflected on this case for some time, is that if Jeremy is guilty - I accept that this is an 'if' - then Essex Police don't come out of this too shabbily. It's rare in Britain for public bodies to admit to an error so openly and put things right. I wish it happened more. Great courage was shown by Essex Police and its officers in owning up to mistakes and then bringing a probable mass murderer to justice.
All that is with the important caveat that when it comes to issues over the ensuing years, such as disclosure and owning up to particular mistakes, Essex Police and certain individual officers have not helped themselves.
Essex Police did corrupt the crime scene. The question is whether or not this was done on purpose. I think they may have moved Sheila's body from the bed, but even if I am right in that suspicion, that could have been for legitimate reasons - i.e. an attempt to resuscitate her. What is not acceptable is then not disclosing this, which again may be for innocent reasons, but when it remains undisclosed and evidence is constructed around a situation that is otherwise, it becomes a cover-up and is serious because it distorts the crime scene.
Has there ever been a miscarriage of justice based on a crime scene staged by the police rather than the perpetrator? I have never heard of such a thing. That is not to say it can't happen and it may be the case here, but if Jeremy is innocent, I would think it much more likely that what has happened is that the crime scene is wildly open to interpretation, and one interpretation, that of Jeremy as the killer, has dominated over the other, that of Sheila as the killer. A conspiracy wasn't necessary.