Close to a year on from her brutal murder, Karen Carter's abandoned Dordogne home is a heart-rending sight. The vast bloodstain left behind in the driveway where the 65-year-old mother-of-four was stabbed to death last April is hidden beneath a carpet of wild grass and dandelions.

But the 250-year-old property she once lovingly restored stands frozen in time behind yellow police cordons, an ever-present reminder that her killer is still at large.

Last week, on the eve of the first anniversary of one of the most violent murders ever carried out in this idyllic corner of south-west France, I returned to Tremolat to speak to those who knew the former teacher.

When the anniversary falls on Wednesday, Karen will be quietly remembered at the community's social hub, Cafe Village, where she spent so many happy moments. But while her framed photograph still graces the wall by the bar, there will be no formal memorial.

Her French lover, 75-year-old retired businessman Jean-Francois Guerrier, who is the cafe's vice-president, has rejected the idea of any official ceremony to mark the occasion.

He has, however, given his blessing to a song, written in her memory by a local musician, being performed. 'He doesn't want to make a fuss,' says a source. 'Not everyone agrees, but it's his decision. Some people don't want it to overshadow village life.'

It's not known if Karen's husband Alan Carter – who was at the couple's home in South Africa on the night she died – will be in Tremolat to remember her. But he told me last week that the anniversary, and what would have been Karen's 66th birthday on Monday, have made it a 'difficult time' for the family.

I also discovered that French police have begun recalling key witnesses. Those reinterviewed include Guerrier, who was the first to be arrested after he found Karen dying on her driveway minutes after the attack on April 29 last year.

One of her closest village friends has also been summoned, as have members of the over-50s women's football team for whom she played.

Some of the questions put to them suggest that gendarmes are again focusing on the romantic intrigues she was caught up in. One of their strongest theories is that the motive for her horrific killing was sexual jealousy.

Karen met Guerrier, who lives alone in a restored farmhouse a five-minute drive from her home, while volunteering at Cafe Village, which is run from a former butcher's shop on the edge of the village that has around 600 inhabitants.

The wealthy widower, a retired Fujitsu executive who once lived in Surrey, remains a popular figure in the village and is often seen with Karen's cross-breed dog Haku, who was a puppy when its owner was killed. She was leaning into the back of her car to pick him up when her attacker struck.

'Her sweet fluffy puppy is now a huge dog,' says a friend. 'Haku is a constant reminder for us all that a year has gone by and we are still no closer to finding out who killed Karen. We don't want to give up but it's starting to feel as if we will never know the truth.'

According to a source who spoke exclusively to The Mail on Sunday last week, Guerrier was recalled by gendarmes just last month.

The grandfather confided that over a week he spent ten hours going back over his evidence with officers at the gendarmerie in the nearby town of Lalinde.

One of Karen's closest friends in the village told me that she, too, received a call from the gendarmerie three weeks ago.

'It was strange because I was asked about my own romantic relationships and how physically demonstrative I'd been in the village with my boyfriend at the time and whether other people knew we were a couple,' she said.

'I got the impression they were focusing on someone local, someone who might have been watching Karen before she was killed or had some kind of sexual grudge.'

Over the past 12 months, this newspaper has stayed close to those at the heart of this crime and returned to Tremolat at key moments during the investigation. Intriguingly, some accounts and recollections do not always match up, something police have found hugely frustrating.

But what is clear is that detectives remain convinced the answer to this murder-mystery lies among the myriad secrets Karen was keeping before her death.

She had told friends she was walking away from her 33-year marriage and, having embarked on a discreet relationship with Guerrier, had decided to make the Dordogne her permanent home.

But at the time of her death Alan, a marine biologist, was unaware of his wife's relationship with Guerrier and after her death spoke of 'a feeling of complete betrayal' at discovering her infidelity.

He told me last summer he had asked Karen 'many, many times' about Guerrier but she told him, 'absolutely not'. Nor did she say anything of an affair when they last met, a month before her death.

Alan has also previously told me that divorce was 'not a fait accompli' and that at the time his wife was murdered he still had hopes they would stay together. 'I said to her, "If you want to do it, it's up to you but I'm not going to be driving it",' he said. 'We talked about it a lot over the previous year.'

One of her friends, a British man who lives in the village, told me last week: 'The big problem was she wanted to live in France and he wanted to stay in South Africa. She was always talking it through with us, saying: "Something's got to give. I have to get out of this marriage".'

The extent of Karen's double life was laid bare just a month before her death when she travelled to Tzaneen in South Africa with teammates from Les Reines du Foot, an over-50s football team.

Guerrier accompanied her on the tour at the last minute. When it finished he returned to France with the rest of the team while Karen flew to visit Alan at their home in the coastal town of East London.

In recent weeks, French police have asked some of the players again about her state of mind on the trip and questioned whether she may have met someone in South Africa who wanted to harm her.

Another source in the village said Karen appeared to shy away from cameras that followed the team and she avoided being photographed or filmed with Guerrier.

The moments leading up to her death are now horribly familiar. That evening Karen had been among 15 guests at a wine-tasting evening at Guerrier's home.

Many there were unaware of the romance between them. Karen left just before 10pm, setting off in her Dacia Duster car with Haku in the back. It would have taken five minutes to reach her home, Les Chouettes. She got out of the car, walked a couple of metres to the front door, unlocked it and switched on the inside light before returning to collect her puppy.

While reaching across the back seat her killer launched an attack of what police called 'exceptional violence'. The first blow hit her before she turned to face her assailant. Of the eight deep knife blows that rained down on her, one penetrated her liver, another her right kidney right through to her spine, another cleaved her aorta. Her right arm was almost severed by the injuries she sustained.

Guerrier, who later told police that he had locked his home and driven down to spend the night with Karen, arrived to find her in a pool of blood on the driveway. He called emergency services and tried to resuscitate her.

He even called Tremolat's mayor and asked him to bring the village defibrillator. He later told a friend that what he saw was 'just gore'.

Guerrier was taken in for questioning and his bloodstained clothes were taken away for forensic examination but, on the basis of what he told them, detectives quickly turned their attention to another villager – 69-year-old divorcee Marie-Laure Autefort.

She was widely known to be obsessed with Guerrier who, according to her own brother, had wined and dined her and taken her to visit chateaux in the Loire. Friends of Guerrier deny this and say she was a 'fantasist'.

The retired care worker, who was born in Tremolat, was detained for 48 hours but released after a search of her car and her house – a ten-minute walk across fields from Karen's – failed to uncover any forensic evidence.

Marie-Laure's brother, Philippe Monribot, told me she was not physically strong enough to have carried out the murder and that the arrest – and finger of suspicion – has destroyed her life.

One of the most baffling features of this terrible case is the absence of evidence left by the killer. The weapon used to kill Karen, believed to be a long-bladed knife, has never been recovered. No match has been found for DNA found on her car door. There are no CCTV cameras in the village and, with virtually no crime in the area before Karen's murder, doorbell cameras are not used here. Sniffer dogs failed to pick up any scent on the road or the extensive walnut groves around Karen's house, suggesting the culprit got away in a vehicle.

Police are puzzled how someone who killed with such savagery could leave no trace.

French Interior Ministry figures show just over 60 per cent of murders are resolved within three months. On average, that figures rises to 70 per cent after a year.

Concerns have been raised, not least from Karen's family in South Africa, about how the original investigation was conducted. Alan Carter told me last summer that the family was 'very frustrated' that nothing was happening. 'It's such a small village,' he said, 'there must be prime suspects.'

A source close to the investigation says there is 'regret' that Sylvie Martins-Guedes, the prosecutor from nearby Bergerac who first led the inquiry, did not instruct gendarmes to tap phones – a popular policing technique – or carry out surveillance of locals who might have a grudge against Karen, rather than pulling people in for questioning.

Three local men have told me they were asked by gendarmes if they had found Karen attractive or had had sex with her.

'Phone taps frequently yield information and obtaining tapping orders from a judge would have been straightforward,' says the source. 'The suspects were not going anywhere and monitoring them would be easy.'

Many in Tremolat still believe the murder was carried out by an outsider.

Those I met last week continue to talk about a contract killer hired by someone connected to Karen's past in South Africa.

This has created a rift between Karen's friends in Tremolat and her family in South Africa who are certain her killer must have lived locally. Alan Carter told me last summer that rumours that he was behind his wife's death were 'absolutely ridiculous'.

He said they stemmed from false claims that he had refused to sign divorce papers served on him by Karen. He was adamant divorce 'wasn't definite' and says that Karen had confided in her sister when she visited South Africa that she 'didn't really want to do that'.

Back in Tremolat, with tourist season underway, most visitors are unaware of the horror. They are drawn to the tranquillity Karen once found here and thought she would enjoy for years to come.