Alexander Palmer remained at large for a week after savagely stabbing Peter Wrighton to death in a frenzied and brutal attack which almost severed the married father and grandfather's head from his body.
Incredibly Palmer, a former soldier, might have escaped the attention of the police altogether had it not been for what turned out to be a crucial anonymous call from a psychologist.
Following the gruesome discovery made by dog walkers Anne and Nigel Precious at East Harling Heath on August 5 last year police had no idea what happened, let alone who had done it or even why.
Police had considered Mr Wrighton's injuries to have been the result of some sort of animal attack and did not launch a murder investigation until almost 40 hours later.
That was after a Home Office post-mortem examination established the horrific injuries sustained by Mr Wrighton had not been caused by animal, but by a knife.
Police, now playing catch-up, were as prosecutor Stephen Spence told Nottingham Crown Court, 'baffled'.
The killing of an 83-year-old much-loved family man who had been out walking his dogs appeared 'motiveless'.
There was a tangible air of desperation to those early press conferences where police chiefs urged members of the public to check bins for the murder weapon - which has still not been recovered.
The public were also asked to send in CCTV or dashcam footage from the area in the hours prior to and following the discovery of Mr Wrighton's body to try and identify a suspect.
Police were overwhelmed by the response from the public who had been left shocked, outraged and in a high state of fear in the wake of the murder.
Hundreds of people contacted detectives with information but one in particular proved to be vital.
A psychologist, who wanted to remain anonymous, called police after seeing media reports of what had happened on the Heath and suggested police take a look at Palmer.
Up until this call the then 23-year-old had not been on their radar at all.
But Palmer would soon become the prime suspect in the case.
The psychologist had been part of a team at RAF Marham that had been involved with Palmer whose mental health issues were triggered after he was the victim of an assault.
Palmer had told mental health professionals that he heard voices, 'Alex' or 'Little Alex', in his head which told him to kill people or himself by attacking the throat.
In particular he seemed to have a grudge against dog walkers and said when he did hurt someone it could be anyone it happened to, just random, but he had thought about what he was going to do.
Following the tip off police were able to establish through mobile phone evidence - and ANPR cameras which had picked up his car registration number L666 AHP - that Palmer had not only been there on August 5 but also about a month earlier on some kind of reconnaissance trip.
The former soldier was arrested a week after the killing.
Palmer's arrest shocked colleagues at Envigo, formerly Huntington Life Sciences, where he had worked for a few months as a trainee necropsy scientist in an animal testing lab where he cut up dead animals, including rats and mice.
He said: 'It's unreal that it was him.
'I can't believe he's gone off and done that.'
'He seemed a bit of a loner. When I think about it his beady eyes just looked at you. It was just a bit strange really.'
'One colleague said that he remembers him saying that he had a collection of knives at home which was very strange.'
The worker said detectives kept coming back for days after Palmer was arrested, taking away his tools and the bin where he put his sharps in a bid to search for a possible murder weapon.
That search has so far proved unsuccessful but while no weapon has been found Palmer was.
And it was largely down to an anonymous call from the psychologist.
It is a call which has not only helped secure justice for Peter Wrighton's family but also lifted the fear which had lingered above East Harling.
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