Files remain open in the hope that fresh evidence and future improvements in forensic techniques will bring those responsible to justice.
Next Monday marks the tenth anniversary of the murder of Lyn Bryant.
On the afternoon of October 20 1998 the 40-year-old married mother-of-two set out to walk the family dog down lanes near her home at Ruan High Lanes, on the Roseland Peninsula.
Less than an hour after she was last seen, her bloody corpse was discovered lying in the gateway to a field. She had been stabbed five times in the neck, chest and back and her throat had been cut.
Police believe the weapon was a small-bladed knife – it has never been found.
Four months later, the gold and tortoise-shell framed glasses she had been wearing were found back at the crime scene. The find fuelled speculation that the killer had returned to the scene.
Millionaire farmer Les Bate, 71, was found dead at the bottom of the stairs of his home in St Kew Highway, North Cornwall on Sunday April 12, 2002. He had been beaten to death about the head and body.
His son Martin found him lying in a pool of blood near the back door.
The Friday night before he was found, he had been seen "flashing his money about" at the Maltsters Arms public house in Chapel Amble. His wallet contained a cheque for £11,000 and around £1,000 in cash.
Mr Bate left the pub at around 11.30pm and drove home along the A39 to his isolated detached farmhouse, Tregilder Farm. When he was found his wallet was missing.
Similarly, the body of 74-year-old widow Joan Roddam was found outside her isolated bungalow in West Downs, on the outskirts of Delabole, North Cornwall.
She was discovered on November 8, 2003, by a police dog handler. She had been suffocated and left face-down in a field in her nightie and dressing gown.
Mrs Roddam, a former hairdresser who lived alone, was found a little more than six miles from Mr Bate's house.
The year after Mrs Roddam's killing, perhaps one of the most unusual murder cases unfolded.
Margaret James, 58, is currently serving a 20-year jail sentence for conspiracy to murder her paganist lover Peter Solheim.
However, her co-plotters have never been caught.
In June 2004, the mutilated body of Mr Solheim, 56, was dragged aboard the vessel the Clairvoyant by two fishermen after they spotted it floating in the sea off Cornwall.
The dead man had been drugged before he was hacked about the body with a blunt machete or axe and hurled into the sea – he did not die from his horrific injuries, but drowned.
Unlike Cornwall's other unsolved murders, the Solheim case did reach court and a "partial" conviction.
During the case at Truro Crown Court it was revealed that Mr Solheim of Carnkie, near Helston, West Cornwall, was a parish councillor who dabbled in black magic and dealt in pornography.
The jury believed the prosecution's case that James, of Porthoustock, on Cornwall's Lizard peninsula, had acted to murder Mr Solheim after she learned he was poised to leave her in favour of his mistress of nearly 20 years, Jean Knowles, of Par, near St Austell.
In her evidence James told the court that she had last seen Mr Solheim when she dropped him off at Mylor Harbour for a fishing trip with a friend called Charlie on June 16, 2004.
Using Mr Solheim's mobile phone she then sent a series of fake text messages from him to Mrs Knowles.
What James did not realise was that the body had already been found five miles south-east of Black Head, on the Lizard peninsula.
Police never believed that James had acted alone and are still hunting her co-conspirators as she has never revealed who they are.
Last on the list of Cornwall's unsolved murders is a triple killing.
On a warm August night last year someone deliberately set fire to the Penhallow Hotel, perched on Newquay's seafront.
The inferno claimed the lives of Monica Hughes, 86, her son Peter, 43, and Joan Harper, 80 – all on holiday from Staffordshire.
Police launched a murder investigation and in May two men aged 44 and 21 were arrested for the second time and bailed to return to Newquay police station on September 2. The hotel's former general manager, Andy Woollam, 42, and his wife Sarah, 36, were also arrested and bailed to the same date.
However, in August the Crown Prosecution Service announced that because of a lack of evidence no-one would be prosecuted. The four were released without charge.
The only officially unsolved murder in Devon is that of schoolgirl Kate Bushell, 14, killed in 1997 in Exeter, although the disappearance of Genette Tate in 1978 also remains unsolved.
Police said: "All unsolved murders are still under investigation.
"Any new information will always be reviewed and acted upon."