The silencer and the DNA, Julie's statements, the fact that Jeremy let his relatives into the farmhouse, the empty cartridges, the spare key, the wills, the blood on the bedroom carpet, Sheila's illness, the Bible, the whereabouts of Nevill when he was first shot, the fight in the kitchen, the order of death, etc, etc.
Well, I don't think the silencer was used but still think he's guilty
What about the DNA? Such experiments were carried out long after items were handled by various people
I find it irrelevant that he let the relatives in - so what?
What about the empty cartridges? But while we're on the subject of cartridges - where did the extra five come from on the counter top?
The doors were bolted so the spare key is irrelevant
What about the wills? He doesn't deny reading them.
What about the blood on the bedroom carpet?
Sheila was on medication for her illness
What about the bible?
The last three points call for assumptions. I think Nevill was on the stairs, don't think there was a fight in the kitchen, I think it was staged. We will never know the order of deaths for sure but I have given you my scenario.