I'm usually very much on the fence when it comes to cases like this, but having watched the documentary and read a couple of articles, I'm convinced he's guilty.
One question - when the forensic investigator said there was nothing in the safe (rather than £16,000 as claimed), has this ever been disputed by the defence?
And when he'd been the victim of an armed robbery the year before, was this proven? I know it must be a very stressful situation, but if I'd been held up at gunpoint before, I'd acquaint myself very well with the security measures in place. But he didn't think to press the panic button and said, even if he had thought of it, he didn't know the alarm was inaudible. Two engineers at the trial disputed this and said that Garbutt knew it was a silent alarm.
There was a lot made of the stomach contents evidence, but it was agreed upon at trial by two other pathologists that time of death could have been as early as one hour before the robbery, but more like several hours (due to the rigor mortis).
If the customer who claims to have heard a woman's voice at 6.45am was correct (which would apparently rule out Garbutt as the murderer) then it's strange that Garbutt never told police that he'd spoken to Diana at this time. It wasn't until a year later when he went to court and had seen the witness statements that he claims to have spoken to her at 6.15am and 6.45am.
Horizon seems like a bit of a smokescreen here. Unless I'm mistaken, the only relevance is that one of the hypothetical motives put forward for the murder was that Garbutt was stealing from the Post Office. But you don't need to establish a motive to find someone guilty of murder. However, I appreciate than he was only found guilty on a 10-2 majority. So perhaps the now contested evidence that he was stealing money was what pushed one jury member into voting guilty. Without it, maybe it would have ended in a retrial.
I don't really understand why such a big deal was made of the iron bar. It wasn't put there by Garbutt, but surely a passer by just found it and put it on the wall?
The reason I'm so convinced of his guilt is that the alternative scenario is extremely implausible. The robber gets in unnoticed by Garbutt as he's unloading his car between 4.30am and 6.30am. He then hides upstairs until some time between 6.45am to 7.30am when he brutally murders Diana as she sleeps. Why? Garbutt doesn't hear a thing. The robber then waits upstairs for at least an hour until the safe is due to open at around 8.30am. He holds Garbutt at gun point, empties the safe and makes his escape without being seen by anyone in the village (there were a couple of reports of a blue car being driven erratically that morning, but the Post Office had been busy that morning and not a single customer nor the woman hanging the washing out in her yard saw the robber). Within the space of less than two minutes the safe is opened, the contents emptied, Garbutt goes upstairs, goes to his wife's bedroom, tries to wake her, finds that she's been attacked and dials 999.
If that's not far fetched enough, then the prime suspect (according to Garbutt's supporters) is a police officer who set Garbutt up for the murder.
I also saw this from a news article during the trial: 'Records kept by the security company which monitored the alarm indicated that the safe could not have been open at the time Garbutt called for an ambulance.' I don't remember that being mentioned in the documentary, I wonder how definite the security company were about that?
Sorry for the far too long post. It's an interesting case. Could he still potentially be released in five years time if he continues to maintain his innocence?