Nothing's impossible,,Andrea,,simply because none of us were there to witness anything,,,and if this is how the case itself was worked out,,then it sure was the most unfair trial to end all trials.
However,my belief that Jeremy is innocent,still stands.
Jeremy is quick to implant in the Police's mind that his sister is "a nutter",yet leaves a loaded gun lying on the settle in full view of the household the previous evening. He had also allegedly tried to get Shiela to handle a gun in front of relatives. From what I have read Sheila did not like guns,she had last handled a gun at a shoot in Scotland in 1979. We have evidence from Pamela Boutflour who spoke to her late on 6th August saying she sounded like a zombie,and Anne Eaton's evidence that Sheila "couldn't put beans on toast".
The phone call purportedly emanating from White House Farm was a means to give Jeremy the chance to blacken Sheila's character and to afford him an alibi of sorts. He knows full well that they are all dead by his own hand;the only way he can be discovered is if the emergency services send an ambulance quickly and manage to resuscitate Sheila,which is why he dallies so long in contacting them.