One of two people did this crime,I'll ask again why couldn't Bamber have done it,what is the reasoning behind his supposed innocence? Is there something not presented to the court which would allow the Jury to reach a different conclusion.
Of course he could have done it, and may well have done, but I'm not sure.
From what I have read (and mostly not on this forum), some people don't believe Julie was telling the truth, some are suspicious regarding the silencer having been found by relatives several days after the murders and after the police had searched the house, some people wonder whether Jeremy was "set up" by relatives who would benefit financially if he didn't inherit, and some do believe that Nevill rang the police and also rang Jeremy, saying that Sheila had "gone crazy" and had got hold of a gun. In addition, some believe that Sheila could physically have committed the murders, some also believe that she was still alive after the police and Jeremy had arrived at the farm.
I'm sure Holly will add more---she has gone into the forensics in great detail, which, I have to admit, I haven't done.