The smiling photograph of a young British woman seems out of place, set in a tombstone in Grottaminarda’s cemetery. Here, in rural southern Italy, is the final resting place of Claire Martin, whose grave lies between those of Italian families whose descendants did not want to talk about her violent death, as one local resident remarks.

On 1 March it will be four years since Martin struggled up the stairs outside her in-laws’ home, clutching her bloody throat and gasping “a man”. She died minutes later from 10 stab wounds to the throat, prompting police to launch a murder investigation. Witnesses were interviewed, wiretaps set up, and two coroners, a blood expert, and a specialist team in Rome tried to piece together what had happened. But 15 months later the case was closed as a suicide.

The news devastated Martin’s parents, Pat and Ray, who are fighting to have the case reopened. “From what we’ve heard, nearly everything points to Claire being killed. Something underhand is happening,” says Pat Martin from the family’s Nottinghamshire home.

The reaction to Martin’s death stands in stark contrast to those of another British woman, Meredith Kercher, who was stabbed in Perugia little over four years earlier. Her murder prompted the world’s media to descend on the picturesque city in central Italy, sparking a high-profile case which reached Italy’s highest court and led to a series of books and at least one film.

More recently media attention was centred on the case of American Ashley Olsen, killed in her Florence apartment in January. The Martins do not understand why the violent death of another British woman has gone unnoticed. Pat Martin has read a book on the Kercher case to find out. “I earmarked lots of paragraphs in a Meredith Kercher book”, she says, “because there were so many similarities.”

Martin’s death in the rural Campania region, about an hour east of from Naples, seemed to quickly fall off the radar. The investigation into her death was flawed from the start, her parents have argued, claiming that significant leads were sidelined and that the crime scene was fundamentally compromised within hours of Martin’s death.

Facebook Twitter Pinterest Grottaminarda, Italy, where Claire Martin died in 2012. Photograph: Rosie Scammell

When Pat and Ray Martin arrived in Grottaminarda on 2 March 2012, they were taken straight to the house where their daughter died. “The only thing you would have known about that being the crime scene was that there was a bit of police tape attached to the front gate,” says Ray Martin.

Claire Martin, 30, had been staying with her in-laws up the hill from the town, working part-time and looking after her one-year-old son while her partner, Diego Mascolo, worked in Frankfurt.

The couple had met while working at a restaurant in Germany 12 years earlier and, in 2006, decided to settle in Mascolo’s hometown of Grottaminarda where they opened a pizzeria. Their restaurant was forced to close within a year, however, over licensing issues, and they both had to find work in other restaurants.

Just hours before she died, Martin had been chatting to her father about plans to move to Frankfurt to join Mascolo, who had been working there as a chef for three months. “Her last words to me were: ‘Tell mum I love her and I’ll talk to her tomorrow’,” Ray Martin says.

An initial autopsy report, by coroners Oto Macchione and Giuseppe Vacchiano, concluded that Martin had been murdered and that her wounds were not compatible with suicide. But neither did they find any signs of self-defence or injuries on her wrists – the latter disproving one person’s statement claiming to have seen cuts on one of Martin’s wrists.

Vacchiano remains certain Martin was murdered. “It’s a problem that I carry inside … That I wasn’t able to make the judge understand how things really happened,” he says.

Days after the coroners filed their findings, Macchione submitted another, shorter, report in which he said it was probable Martin had stabbed herself – although she may have been murdered. Macchione was not immediately available to comment on why he became doubtful of the cause of death, though Vacchiano says his colleague’s change of opinion struck him as strange, as did the judge’s remarks on suicide.

He said that when he went to see the judge about the investigation, the judge said: “Check, are we sure that it wasn’t a suicide?” Vacchiano found this odd: “I have never forgotten this phrase,” he says.

The judge in question, prosecutor Michela Palladino, says she had set out looking at a murder investigation until evidence proved to her that Martin had killed herself. “There weren’t all the marks [on her body] that there should have been ... if she had tried to defend herself in some way,” Palladino says. “The was the fundamental thing.”

Neither coroner had access to the 33cm kitchen knife found at the scene and had to rely on photographs of it during the autopsy. In coroner Macchione’s second report he concluded Martin could have killed herself, as the knife was so sharp it would have required minimum force to cause the wounds on her neck.

“It could have been sunk in more times, also without causing excessive pain, because [it was] pointed and sharp,” he found. The authorities concluded Claire Martin had taken the knife from her flat in the centre of Grottaminarda.

Ray and Pat Martin had visited their daughter about two months before she died, staying in her flat for two weeks. Ray is certain that the knife was not from Martin’s apartment. His view is backed up by a wiretapped conversation, in which someone who had worked often with Martin’s partner, a chef, said the knife was not Diego Mascolo’s.

Vacchiano believes Martin was carrying a knife for self-defence when attacked. “I think the woman lived in a condition [in which] she was scared of something or someone,” he says. The coroner explains her wounds, inflicted from both left and right, as signs that she tried to defend herself against an attacker who overpowered her.

When the autopsy was carried out, the knife was sent to be analysed in Rome by the scientific police, who were also involved in the Kercher case. Investigators in the Italian capital found a component of male DNA on the handle of the knife, but said it was “not useful” for future comparison.

The overall analysis concluded that Martin had committed suicide, based on factors including the lack of space for an aggressor to operate in the small ground-floor area outside the house where she is believed to have sustained her injuries. They also found that Martin would have had 10 to 15 minutes to find help after being injured.

Martin, bleeding from her wounds, had climbed the 21 steps to her in-laws’ home. It was there that, according to her mother-in-law’s testimony, Martin said “a man” and gestured to signal her attacker had escaped towards the land above the house. She repeated the phrase, “there was a man”, and died after the arrival of other family members and before an ambulance crew reached the house.

Maurizio Saliva, the forensic medicine and blood pattern expert who arrived on the scene 19 days later, concluded Martin had killed herself. “I have no doubts,” he said. “Because I remember the type of injuries, some of which were parallel, and so they were very probably test cuts.”

Saliva says that he has frequently seen test cuts in suicide cases, although never before in the throat. Saliva also says he relied on photographs taken at the scene and viewing the body to reach a conclusion of suicide, as most of the blood had been cleaned up hours after the stabbing and Martin’s clothes had been destroyed.

James Fraser, director of the University of Strathclyde’s Centre for Forensic Science, says that care is needed when relying on photographic evidence, as fine spots of blood may not been seen and 2D images can be misleading if taken at an angle. “You don’t tend to get many blood patterns from stabbings; what they’re looking at is drip patterns,” Fraser says, giving the example of an attacker holding a weapon over their victim. “It’s not clear to me how you could determine from a blood pattern how it could be a suicide.”

Vacchiano finds it unusual that he was not informed in advance that Saliva would be joining the investigation. “In my opinion, it was as if they wanted to close the case quickly,” he says.

In Grottaminarda, police supported the suicide theory with testimony from local people who said they had noticed Martin was missing her absent partner and had lost weight – by some accounts following a diet – and was worried about the move to Germany. Those interviewed by the police had described Martin as a doting mother. She was held in high regard by people in the town.

Facebook Twitter Pinterest Claire Martin’s parents, Ray and Pat. Photograph: Martin family

Liz McDonald, the chair of the perinatal faculty at the Royal College of Psychiatrists, says women can be good at concealing symptoms of postnatal depression from their families, even a year after the birth of their baby. “The striking thing about postnatal suicides is that they’re violent. The person wants to make sure that they complete it, they don’t want to take any chances about surviving,” she says.

Martin’s family are adamant that she was not suffering from postnatal depression and, despite any apprehensions about the move, she was looking forward to life in Germany.

They claim the Italian investigators failed to follow – or ignored – leads to find Martin’s killer. CCTV footage from a nearby hotel is said to show a man walking in the direction of the house a few minutes before Martin died, though the man was not identified. Police asked local residents whether Martin had ties to men other than her partner – the general response was that Claire was committed to him.

As part of the investigation, a series of wiretaps were set up on local phone lines and rooms were bugged. While the transcripts show people discussing suicide, there are also questions that appear to support the murder theory.

People talked about someone hearing screams, while another person named a suspect and threatened to “burn him alive” if he turned out to be Martin’s killer. “That son of a bitch,” a man responds on being told how many cuts Martin sustained. “Let’s hope that it’s him,” one person said on another occasion.

The transcripts are also filled with people telling each other to “shut up” and keep quiet, discussions about the need to get lawyers and a person fearing they would end up in prison. “We need to talk, otherwise they will blame us,” someone says.

Judge Palladino says all leads were followed up and alibis checked. Investigators also looked into Martin’s finances and found she had no life insurance policy and there had been no suspicious transactions from her bank accounts – although questions remain about the role of money in the case.

A handbag found under Martin’s body was taken by police, who listed its contents without mentioning a significant amount of money.

A week after her death, however, two people were heard in a wiretap discussing Martin’s case and €700,000 in a bag. “No one touches the money,” one man said, later adding: “OK, when we finish we’ll go to the station in Grottaminarda, and say that there was €700,000 inside the bag.”

In other conversations, a person described police as being “fixated about the problem of the money”, while at another point someone says, “it’s necessary for the wife to take the money”.

In discussing the wiretaps with the Observer, Palladino said she did not recall the specific conversation referring to €700,000.

She said investigators also examined the theory that Martin’s death could have been linked to the criminal underworld in the Campania region, home to the Camorra mafia. “Places in this part of Italy, in a certain sense there could be infiltration, connections, but there was no specific element that we could look into.” Once Palladino ordered the case closed, a second judge, Gelsomina Palmieri, heard the Martins’ objection in 2014 and ruled there was no reason to reopen the investigation.

Pat and Ray Martin have since tried diplomatic channels, meeting the UK’s minister for Europe, David Lidington, and asking him to press for the case to be reopened. The office of Sandro Gozi, Italy’s undersecretary for European affairs, says Gozi had not been involved in the case and has no authority in such an area.

The Foreign Office said in a statement that it “cannot interfere in the legal system of another country”, although Ray Martin says the government has done so in the past. He cites the case of Neil Heywood, a British businessman found dead in China, which saw the direct intervention of David Cameron.

Nottinghamshire police are unable to intervene in the case unless invited by Italy, although there are plans for an officer to travel with Pat and Ray Martin to meet Palmieri later this year.

At home the Martins have been supported by their Labour MP, Gloria De Piero, who joined the family in a meeting with Lidington and is asking that funds be released to translate case documents.

“Since the moment Mr and Mrs Martin came to me with the terrible story of their daughter’s death, I have felt that there were many questions that the investigation left unanswered,” De Piero said in a statement.

“Understandably, the Martins want to know exactly what happened to Claire and will not rest until they do. I urge the government to help them get the answers they strive for.”

The Martins hope that, in digging deeper into what they see as flaws in the initial investigation, the Italian authorities will be compelled to take a new look at their case. There is also the possibility of uncovering evidence to spark another investigation, which has happened in previous cases in Italy.

“I feel there’s been a complete injustice,” says Ray, rolling off a series of questions about what happened to his daughter. Pat says it is time they had the answers: “We have to have some kind of closure, we don’t think we’re ever going to get it. We just want to know the truth.”