There is no direct evidence that Jeremy Bamber was the killer. The point is that the case against him is entirely circumstantial, but includes forensic evidence. (The point is slightly contentious because you could argue that Julie Mugford's evidence is direct evidence. I would disagree, but even if we concede the point, there is still no direct forensic evidence).
I also agree that the crime scene was compromised by the police, but that was not at Jeremy's instigation and so could be seen as a neutral point, since the police may well have destroyed evidence that could have exonerated him. It is also worth noting that the carpets were only cut up after blood samples were taken.
Unless the blood spots you mention came from several victims, I doubt it would be of much significance as it could easily be put down to contamination of Jeremy's clothes.