The defence are not obliged to disclose anything. It is for the prosecution to prove guilt, and that comes with an obligation to make full disclosure.
Yes I know, that doesn't mean they didn't have anything that influenced their handling of the defence. Afterall, at the end of the day lawyers are people too and would surely have the same level of disgust for such a crime and the perpetrator? Especially if they have knowledge that Bamber was likely guilty?
Sure, they could have pursued the RB blood in the silencer theory, however, if I were a member of the jury, it wouldn't be enough to tell me he had the same blood group and enzyme as Sheila - I don't even know what my own blood group is so the first thing I would wonder, would be how he could have known? There isn't a single reason why he would. I also imagine that drawback wasn't something he would have been familiar with. The only way that would have worked, is if the police identified the two samples as being the same and used his blood to contaminate the silencer given that Sheila's samples were sealed. Not that I'm trying to add to the whole idea of a conspiracy!