At 4.30am on 22 November 1995, taxi number 69 pulled into the Campsa Red petrol station in La Constancia, a scruffy neighbourhood in the centre of Jerez. The driver stopped at pump 1, got out of his car and dragged the nozzle to its fuel inlet, but the pump wouldn’t turn on. When he went to look for the attendant, he saw that the door to the station’s shop had been smashed. Magazines and papers were strewn across the floor. Then the driver noticed blood on the shop’s walls, and ran to a payphone to call the emergency services.

Within minutes, municipal police arrived. One of them found a trail of blood, which led to an office behind the cash register. When the door to the room wouldn’t open, they forced it open. Barricaded inside, behind a photocopier, a young man lay slumped on the floor, inert and bleeding heavily. He was still breathing.

Five minutes later, a team of paramedics crammed into the cluttered office. Covered in blood and surrounded by medical equipment, they tried to staunch the young man’s wounds. But by 4.45am, Juan Holgado was dead.

Just after 5am, Manuel Buitrago, the acting magistrate who would oversee the criminal investigation, arrived at the petrol station. Buitrago, who was 41 and had never handled a murder case before, immediately ordered a thorough inspection of the premises. Investigators found a large juice carton stained with blood, a button ripped from a raincoat and a pendant engraved with the sign of Virgo. They collected 23 fingerprints from the scene, though at this stage it was impossible to know whether any of them belonged to the perpetrators or to the customers who had entered the petrol station that day.

The shop floor and office had not been cordoned off, and as word of the murder spread, the crime scene became increasingly chaotic. By 5.30am Buitrago found himself surrounded by paramedics, consultant criminologists, police officers and local journalists. While they trampled over one another, and sometimes the evidence, investigators were picking up crime-scene debris without using protective gloves.

The initial inspection of Juan’s body by a forensic scientist took place at 5.50am. There were 30 stab wounds in total – some relatively superficial slices across his face and hands, others deep gashes to his chest and the backs of his legs. The coroner later determined that they had been inflicted by an 18cm blade, like the ones used for carving Spanish ham.

To Buitrago, the violence of the attack suggested two or more male assailants. Records from the petrol station’s cash register showed that someone had bought the juice carton and a pack of cigarettes at 4.02am, but there was no CCTV footage and no witnesses. Prosecutors would later conjecture that Juan’s killers had encircled him, slashing the backs of his legs so that he couldn’t run away, and then knocked him to the ground. Juan somehow managed to scramble to the small office at the back of the shop, but the attackers forced their way in and continued to stab him. There was no obvious motive. It seemed that Juan, who was 26 years old and had never been in trouble with the law, had simply been in the wrong place at the wrong time. He had even swapped shifts with a colleague that night.

Buitrago soon came to suspect that Juan’s attackers were drug addicts. By the beginning of the 1990s, Spain had become the primary entry point for the cocaine trade in Europe, and Jerez, 30 minutes north-east of the Bay of Cadiz on Spain’s southern coast, had begun to suffer from drug-related crime. There had been a series of recent robberies carried out in and around Jerez by the “Harpoon gang”, a criminal group that specialised in attacks on petrol stations. But the work of this gang had been efficient and professional, while the robbers who killed Juan seemed desperate and careless. They had ransacked the shop and failed to break open the station’s safe, making off with just 70,000 pesetas (480 euros) from the till.

It took Buitrago six weeks to detain the first suspects. The three accused were known criminals with a history of robbery and drug-dealing. (A fourth suspect was detained several months later.) Three of the four men had criminal records, and all four were known to the police as consumers of hard drugs. They all vehemently denied the charges against them.

News of the arrests soon made its way into the local press, and on 15 February 1996, they said the case was close to being solved. But for the victim’s father, Francisco, and his family, it was the beginning of a nightmare that has never ended.

When Francisco Holgado first learned of his eldest son Juan’s death, he reacted as many suddenly bereaved parents do. “I never believed that something like this could happen to me,” he told me recently.

For most of his adult life, Holgado had been a bank clerk. To his friends and neighbours, he was the respectable patriarch of a normal, middle-class family – husband to Antonia Castro, and father to their three boys and a daughter. But the murder changed him: “I was an ordinary man who was forced to unbelievable extremes,” he said.

In the months following the killing, as Spanish authorities struggled to solve the case, Holgado, then 51, grew increasingly obsessed with identifying his son’s murderers. Over the next two decades, his pursuit of justice came to consume his life. The Spanish press, upon discovering his story, championed his cause, and nicknamed him padre coraje, or father courage. But as the media portrayed him as a hero and the embodiment of paternal love, his own family was falling apart, and would eventually abandon him.

Today, two decades after his son’s death, Holgado looks younger than his 73 years, but talks with the tremulous voice of an old man. He is bald, with olive-coloured skin and a long, drawn face. He still dresses in black, and lives alone in government housing on a narrow, cobbled street in Jerez’s old town, surrounded by shabby, whitewashed townhouses and crumbling baroque mansions.

Facebook Twitter Pinterest Francisco Holdago with a memorial to his son Juan at the petrol station where Juan was murdered. Photograph: Aitor Alcalde

Every morning he wakes up at 7am in his small, dark bedroom. After breakfast, he goes to a local cafe to scan the newspapers. From here, he normally cycles to the cemetery to visit the grave of his son, to clean his tombstone and replace the flowers.

One afternoon this spring, Holgado interrupted his routine to take me to the neighbourhood of La Constancia. Passing through streets of anonymous high-rise blocks, Holgado stopped at a busy roundabout and pointed to a petrol station. Cast in the familiar red, orange and white of the Spanish petroleum giant Repsol, the building looked unremarkable. To Holgado, however, this is the place where his life fell apart – a memorial to his family’s suffering and to his attempts to make such suffering go away – which, in turn, only led to more suffering.

“I wonder what all the people who pass by would think if they knew what happened here 21 years ago,” he said. “And all that I became as a consequence.”

In the weeks following the murder, the Holgados grew increasingly angry about the lack of answers from the police, who had promised the family a speedy resolution. On 21 December 1995, three weeks before Buitrago made his first arrests, they rallied 3,000 people from all over the city for a “justice march” through Jerez’s historic quarter. Friends, politicians and strangers paraded through the narrow, serpentine streets of the old town, while neighbours yelled encouragement from windows and shopfronts. The following day the headline of the local newspaper, El Diario de Jerez, read “Weeping for Juan”.

The savagery of Juan’s murder had shaken many inhabitants of Jerez, where, despite the drug problems in the city’s poorer barrios, an atmosphere of conservative Catholic gentility still prevailed. “I remember everyone was talking about it,” Joaquin Rodriguez, a nurse and lifelong Jerez resident, said. “It struck many families that it could have been their own son.”

As the investigation dragged on through the spring and summer of 1996, with the prospect of a trial looking increasingly distant, the Holgados stepped up their demonstrations. Francisco Holgado visited the local constabulary every day to get the latest updates and he often joined Antonia in front of the magistrates’ court, where the pair would protest next to a large poster criticising Buitrago’s decision to release the defendants on bail. On the 22nd of every month, they held a rally in the city’s main square, calling for justice for their son.

From the moment it began, the official investigation into Juan’s murder had been a disaster. “The police entered [the crime scene] like bulls in a china shop,” José Luis Fernández Monterrubio, the head of the Jerez police at the time of the killing, would later admit. In autumn 1996, senior murder investigators from Seville joined the case, and uncovered further blunders by local police. Crucial evidence, such as the bloody juice carton, had been lost, and it emerged that several witness testimonies had been made under duress. The local paper began criticising the police and attacked Buitrago, claiming he had been sanctioned by the Spanish ministry of justice for the unnecessarily long time he had taken to investigate two previous cases. Buitrago would later claim that the criticisms of the Jerez police were exaggerated, telling the local television channel La Sexta, “Whoever arrived at the crime scene that day would have done the same thing. It was the way cases were worked back then.”

The coverage made Holgado even more sceptical of the authorities. On a visit to Juan’s grave in the sprawling, dusty cemetery of Nuestra Señora de la Merced on the city’s outskirts, he made a promise to the son he had lost. “I told him I would see his case through to the end, no matter what I had to do, no matter what the consequences,” he recalled. If the police would not solve the case, Holgado decided that he would.

By the beginning of 1997, two years after the murder, Holgado was living a double life. Every weekday morning at 6am, a bus picked him up to take him to his office in Seville, 60 miles away. He slept on the bus, worked at the bank until late afternoon, and came home to change his clothes. Then, several nights a week, he went out to wander through Rompechapines – a once-salubrious area of Jerez that had turned into a drug neighbourhood – desperately hoping to dig up any information related to the murder of his son. Until the early hours of the morning, he would visit smoky bars frequented by pimps and brothels in abandoned townhouses.

His early expeditions were “impromptu, very off the cuff”, Holgado told me. This was not wholly out of character. He could be an impulsive man. Once, in his 20s, when stationed in north Africa on military service, he had slapped a superior officer across the face during a game of football because the man had spoken to him rudely. Even after becoming a father, he always took opportunities where he thought he saw them, in spite of the tensions it caused at home. In Jerez, he moved his family from home to home – more than 10 times in 10 years – always searching for new properties that he thought were bigger and better. “He could be quite self-absorbed,” Paco, his second oldest son, told me.

Slowly, he became more organised and began pursuing leads he that picked up in the local press or from police officers with whom he was friendly. At crack dens in Rompechapines, Holgado had long conversations with half-stupefied junkies, who he enticed into conversation with cigarettes or tablets of Tranxilium, a tranquilliser prescribed for the chronic anxiety he had been experiencing since Juan’s death. While his subjects got high, Holgado smoked cigarettes and recorded everything on a Sanyo dictaphone he carried in a plastic shopping bag. At one point, a drug dealer he tried to interrogate threatened to put a hole in his chest with an industrial road drill if he didn’t stop with his questions.

Facebook Twitter Pinterest Francisco Holgado in 2010, marking the number of years since his son’s murder on a protest banner outside the petrol station where he was killed. Photograph: Miguel Gomez/AP

On the weekends, instead of spending time with his family, Holgado would sit down to review his recordings. Usually, what he heard disappointed him: meaningless names, fanciful stories and dead ends. “Whatever made him think that he could better the efforts of a fully funded state police force was something I always found strange about Holgado’s escapades,” Manuel Hortas, a lawyer for two of the defendants, told me.

Holgado believed that what was holding his private investigation back was not his lack of expertise as a detective, but his local fame. Francisco’s face had been plastered across front pages, his “bravery in the face of tragedy” repeatedly lauded in El Diario de Jerez, his voice broadcast to listeners of the local radio station. He tried using fake names during his nighttime sorties, but he was often recognised.

One afternoon in late 1997, Holgado was at a cafe in the barrio of Asunción when a tall, spindly man with wild hair and an ill-fitting suit approached him. The man introduced himself as Pepe el Gitano (Pepe the gypsy). He told Holgado that he had some important news related to Juan’s case. If he wanted to hear it, they would have to meet later at a secret location.

Pepe never showed up at the rendezvous point. After months of investigating, Holgado was used to such disappointments, but Pepe lingered in his mind. It struck him that, in Jerez’s underworld, unknown people seemed to appear and disappear all the time. Why couldn’t he do the same?

At the end of March 1998, Holgado joined the queue of a methadone clinic in the Asunción neighbourhood. He wore a leather jacket, baggy jeans, a blue denim shirt and large tortoiseshell sunglasses. He also wore a medium-length wig, with dark brown hair parted at the side; affixed to his head, it looked like the clip-on hair of a Lego character. Introducing himself as Pepe, he began striking up conversations with addicts by offering a 50,000-peseta reward for a fictitious lost dog named Rufo.

After meeting Pepe, Holgado had decided that rather than interview people at random, he would focus his intelligence-gathering missions on the four suspects, who had been charged with murder but whose trial was not scheduled until the following year. He believed the police had the right men, but he did not trust them to uncover the necessary evidence for a conviction.

Holgado knew it would be impossible to follow all four defendants at once; they moved in similar circles, but as one of them would later claim, “we barely knew each other”. Two of the men were in and out of prison for other crimes, and another suspect had proven difficult to track down. Holgado had learned through local newspaper reports that the fourth suspect, Pedro Asencio, had stayed in Jerez since the murder, a requirement of his bail conditions, at the house of his blind father in Asunción. Asencio, who was 35, had a long history of heroin abuse and petty crime, and people who knew him had told Holgado he could be unpredictable and violent.

Holgado found Asencio at the methadone clinic, standing in the queue, his hands shaking from withdrawal. Holgado offered him a Tranxilium tablet and a cigarette to ease his nerves. The two men struck up a conversation, and Holgado told Asencio that he could get him more drugs if he wanted.

Facebook Twitter Pinterest Francisco Holgado in the disguise he used to infiltrate Jerez’s criminal underworld. Photograph: Manuel Pascual/AP

As the spring crept on, Holgado – always posing as Pepe – contrived more meetings with his mark. He would offer Asencio, who couldn’t drive, lifts in his car to visit his friends, to buy drugs and even to see his daughter, who was living with his ex-wife outside Jerez. Asencio, who was normally a very suspicious person, was charmed by Holgado. “I had been looking for ways to make quick money so I could take care of my daughter,” he later told the newspaper El Mundo. “What Pepe was offering me was what I was looking for.”

The more time the pair spent together, the more elaborate Holgado’s fictional identity became. He told Asencio about a gang he was connected to, which moved large quantities of cocaine through the north. He even employed the help of another local junkie, Jaime Monje Rodriguez, who, using the pseudonym Carlos, posed as Holgado’s gang contact.

Nearly two months into Holgado’s undercover operation as Pepe, Asencio told him that he suspected that Domingo Gomez and Francisco Escalante, his fellow defendants, were involved in the murder at the petrol station. Asencio claimed that he had seen Gomez give Escalante a bag of bloody clothes to throw in the bin a few days after the murder. “When Escalante saw the bag, he got spooked, and started yelling at Gomez to get rid of it,” Asencio said in a recording that would later be played in court. He told “Pepe” he hadn’t had any involvement in the crime himself. (Gomez and Escalante have also always maintained their complete innocence.)

By mid-1998, Pepe and Asencio were meeting two or three times a week. Around this time, Holgado quit his job at the bank; he could no longer work and investigate his son’s murder at the same time. He was just about keeping his anxiety in check with antidepressants, but his relationship with his family was becoming increasingly strained. Even before Juan’s death, his marriage had been fragile. Now, things were deteriorating under the strain of grief, with Antonia’s feelings about her husband’s late-night trips varying from day to day. Sometimes she would encourage him; other times, she could not understand why he went to such extremes. “I was uneasy about his trips,” she told me. “I, too, wanted justice for my son, but Francisco always had to make things unnecessarily difficult, and he had to do them his way, no matter what.”

Their son Paco, who had occasionally accompanied Holgado on his investigative trips before he assumed his undercover identity, agreed with his mother. He believed his father’s new endeavours were too dangerous, and probably futile. (The only other person who knew of Holgado’s double life was the family’s lawyer, Juan Pedro Cosano, who was supportive. “I thought it was an extraordinary act of bravery and love,” Cosano told me.)

Holgado’s life was not only coming apart; it was also in danger. According to Holgado, one day that summer, Asencio told Pepe he was going to kill Juan Holgado’s father. He had heard a rumour that Francisco Holgado, tired of constant delays in his son’s case, had bought a shotgun and was going to hunt him down. Asencio said he would get the old man first.

Holgado was dumbfounded, and in a moment of panic, he offered to do the job himself: Pepe told Asencio that he would murder Francisco Holgado to save his new companion from getting into further trouble.

“I saved my life by proposing to kill myself,” Holgado told me.

Despite the catalogue of errors committed by investigators in the wake of Juan’s death, they eventually built up sufficient evidence to bring to trial the four original suspects – including Asencio – who had been arrested six weeks after the murder.

In the days preceding the trial, Holgado sat down with his lawyer, Cosano, to sort through the 12 tapes he had recorded during the eight months he had spent undercover as Pepe. Holgado knew that such secrecy might pose legal problems, but it was a necessary risk to extract as much information as he could from Asencio. “We decided to hold the tapes back for the element of surprise,” Cosano told me. “We knew it was going to be a difficult trial and we needed to use every trick we could think of.”

On Monday 11 January 1999, the four defendants entered Cadiz’s Audiencia Provincial courtroom in handcuffs for the first day of the trial. When called upon to speak, Asencio, dressed in a brown, grey and white striped shirt, denied his involvement in the crime or any connection to Juan Holgado.

After Asencio had batted away a few further questions, Cosano asked: “Did you know that the person that went by the name of Pepe was, in reality, the father of Juan Holgado?”

Facebook Twitter Pinterest Francisco Holdago with a picture of his son Juan. Photograph: Aitor Alcalde

Red-faced, Asencio said that he did not. But Cosano wasn’t finished; he then announced that his client had recorded hours of his secret conversations with the defendant. The courtroom reacted with astonished murmuring.

“It’s a moment I will never forget, the look on Asencio’s face when I told him, the reaction from the gallery when I mentioned the tapes – it was like something out of a Hollywood film,” Cosano said to me. (In a 2003 interview with El Mundo, Asencio claimed he had known of Pepe’s real identity before the trial.)

The judges stated they would need time to consider the admissibility of the audio evidence collected by Holgado. In the meantime, as the trial continued, the critical importance of the tapes became clear: there was a lack of physical evidence, such as fingerprints or traces of blood, to tie the accused to the murder; on the stand, several key witnesses retracted their earlier statements, including a prostitute who had confessed to seeing the blood-soaked suspects the night of the murder.

Then, on day four, the judges announced their decision on the tapes: they would not be admitted as evidence, as they lacked “legal guarantees of authenticity or integrity”. The case for the prosecution was looking increasingly thin.

Holgado had gone undercover to solve his son’s murder, made friends with one of his son’s alleged killers and pledged to kill himself in order to save his own life. Now, midway through the trial, Francisco Holgado became a household name across Spain. But such renown would come with a price.

On Sunday 17 January, El Mundo published a profile of Holgado with the headline “Padre Coraje”. The article, written by a local journalist, Pepe Contreras, extolled the virtues of a father who had risked his own life to secure justice for his son. The writer, who spoke to Holgado at his home, focused on the bank clerk’s “sangfroid” in the face of danger, and the “rage” that allowed him to meet Asencio day after day. It turned the Holgados into celebrities overnight.

At the time, Antonia was not only dealing with the death of her son, but also recuperating from illness. Now, suddenly, her husband was a national hero, and the media were camped outside their house hoping for a word with Padre Coraje. Spain’s biggest newspapers and TV channels all wanted to hear his story. So, too, did the foreign press. (The Argentinean broadsheet El Clarín published an article about the case, describing how an Andalusian bank clerk “had pretended to be a criminal to seek justice, not vengeance, for his deceased son.”) Holgado seemed to excel in front of the microphone, and never demurred from discussing the details of his own heroism.

The next week, the defence and prosecution rested their cases, and the judges retired to consider their verdict. On 9 February, while Holgado was speaking to Portuguese journalists who had started making a documentary about the case, the judges announced their verdict: all of the defendants were acquitted.

Holgado was distraught, but now he had the nation’s attention, and as long as he held it, he thought he had a way to fight the court’s verdict. On 20 February, while his lawyer launched an appeal in the courts, Holgado locked himself in the petrol station where his son had died, threatening to burn the place to the ground if the company didn’t provide safer working conditions for its employees. Along with his daughter, Maria, he also graffitied public buildings with slogans such as, “Juan Holgado’s murderers still at large in the street,” and “Justice for Juan Holgado”.

Behind such shows of public unity and the idealised images of the family that appeared in the media, the Holgados were coming apart. Paco told me that he and his siblings sometimes felt that their father was being consumed by guilt at having been emotionally absent in the years before Juan’s death. “He had never really been affectionate with any of us before my brother’s passing,” Paco told me. Now he was absent again, immersing himself first in his undercover investigations, and then in talking to journalists. He had barely noticed when his son, Paco, left for Germany to work in a casino, at the beginning of 1998. Nor did he see how much his other children were struggling to cope with their brother’s murder.

Facebook Twitter Pinterest Antonia Castro, mother of Juan Holgado and wife of Francisco, facing the press in 2003. Photograph: A Movellan/EFE

Antonia felt that in interviews with the media, her husband exaggerated his bravery. “He never put himself at as much risk as people say,” she would later claim. “When he went to meet with Asencio he was always accompanied by someone else, even when he said he was alone,” she told me. She also believed he lied about the unity within the family, and stole the spotlight for himself rather than shining it on Juan’s case. She, too, had campaigned relentlessly for justice, organising marches and visiting the police station on an almost daily basis. “I never sought out media acclaim for all the sacrifices I made,” she told me.

In early 2000, the rift between Holgado and his family became unbridgeable when he sold the rights to a book and a TV drama based on Juan’s case. While Holgado travelled to Madrid to negotiate the contract with the national TV channel Antena 3, Antonia was in hospital, receiving treatment for an embolism in her lung. She had opposed the idea of a film, but now, bedridden, she was powerless to stop it. Holgado told his family he had only made the deal because the TV channel said it would shoot a film with or without his consent, but they didn’t believe him. When Holgado brought home some 6m pesetas from the deal (€36,000), Antonia accused him of taking advantage of the family’s suffering. “He prostituted his own son’s death,” she told me.

The film, entitled Padre Coraje, was first broadcast in March 2002. It depicted the Holgados as a family guided through their suffering by a brave, humble patriarch who had rubbed shoulders with a lurid cast of characters from Spain’s underworld in order to hunt down his son’s killers. Asencio, for one, believed the interpretation of his character was greatly exaggerated. “The king of the blade, ‘el Maquea’, and all that rubbish,” he told El Mundo, referring to the nickname that the screenwriter had given him.

Antonia could not bring herself to watch the film, but she saw its repercussions. Her life and her suffering were gossiped about over coffee in terraces all over Jerez. “I hated that people were entertained by our sadness,” she said.

In 2000, the supreme court of Spain had accepted the family’s appeal and granted a retrial. Through October and November 2003, Holgado’s tapes were played to a full house in the same courtroom where his son’s alleged killers had been tried and acquitted nearly five years earlier. The same four suspects sat on the same bench, but now the public gallery was packed not just with the local papers but with journalists from El País and El Mundo and TV cameras from all the leading channels. Francisco Holgado stood at the back of the courtroom, his chest puffed out. “I was positive that this time around, things would go right for us,” he told me.

What followed on the tapes, however, were hours of drunken slurs in bars and unintelligible mumbles in the back of cars. For all Holgado had done to befriend and solicit information from Asencio, the younger man never confessed to the crime. The prosecution struggled to put together a credible narrative from the jumbled recordings, and on 3 December, the four suspects were again acquitted of murder.

Stuck in limbo, with little hope of bringing their son’s killers to justice, the family rapidly disintegrated. Holgado and Antonia divorced in 2004, but continued to lash out at one another, their disputes unfolding in the public eye. Antonia told the papers that her husband had never loved Juan and that he was a bad father. All three children sided with their mother and gradually broke off contact with Holgado, who claimed that they had been turned against him by their mother.

After their separation, Antonia and Holgado began to campaign individually. When, in 2006, the supreme court rejected a second appeal for a retrial of the same defendants, Antonia started a series of hunger strikes outside the petrol station where the murder had taken place, while Francisco again painted slogans on government buildings and police stations. Both parents continued to visit the police station each week for updates on the case, and both spent time offering support to other families who had lost children to violence.

With no new evidence or impending trial, the public and the press lost interest in the Holgados. The abandonment made Holgado feel hollow and alone – in the absence of his family he had always had the love of the public. Now they too seemed distant. “I realised that people had to get on with their own lives,” he told me. According to Paco, the canonisation of his father made Holgado accustomed, perhaps even “addicted”, to his saintly image. When the press lost interest, Holgado felt he had to strive even harder to catch its attention, to be deserving of the name Father Courage.

Facebook Twitter Pinterest Francisco Holgado holds up pictures of his murdered son during a football match in Jerez in 2010. Photograph: Cristina Quicler/AFP

On 23 December 2008 Holgado stepped on to the tracks at the Jerez central station. In front of a stationary Barcelona-bound train, he laid out a large white poster that read, “Juan Holgado, 22-11-95, 13 years without Juan, 13 years without justice. Police and Judges: useless. Why?” He then sat on the track for 40 minutes, accompanied by a handful of local sympathisers, until he was dragged off the tracks by the police.

Less than a month later, on 11 January 2009, 30 minutes into the first half of a La Liga football match between Xerez and Tenerife, Holgado skipped over the barriers of the spectators’ area at the Chapín stadium in Jerez and ran on to the pitch. He carried a white carnation and the same white poster. In front of 7,000 fans and national TV cameras, two senior players, one from each side, escorted him off the pitch to rounds of applause. “What this father has suffered is unimaginable, and we must support him in any way we can,” Antonio Calle, captain of Xerez, told Canal TV after the match. (He would repeat the same stunt at another match the following year.)

In May 2009, the police closed Juan’s case, citing a lack of new evidence. The local papers wrote about the event as if it were the end of the story, but for Antonia and Francisco the story would not be over until the killers were behind bars. “You just knew they were never going to throw in the towel,” Antonia Asencio Garcia, a senior politician for Socialist Party of Andalucia and acquaintance of the Holgados, would later tell the Spanish press.

In October 2015, Holgado arrived in Madrid on foot, limping slightly and wearing a white T-shirt emblazoned with a portrait of his son. The 71-year-old had walked 600km from Jerez, along busy motorways and dusty country roads, to seek an audience with the acting minister of justice, Rafael Catalá.

The preceding six years had been tough. No new evidence had emerged. Holgado had been suffering from heart problems, and had attempted to sue Antonia for harassment, after taking a restraining order out on her in 2009. He had never given up campaigning for his son, but making any impact had become difficult. As the date of his son’s case neared its statute of limitations, which for murder is 20 years, Holgado knew he had to do something dramatic.

Holgado could have flown to Madrid to see the minister, but he wanted his efforts to capture attention, and to be more media-worthy, and so in early 2015 he came up with the idea of a justice march. But rather than just a march for Juan, Holgado envisioned a protest for all those families caught in limbo, who still didn’t know the identity of the criminals who had killed their loved ones.

Holgado’s lawyer, Jose Miguel Ayllon, who had replaced Cosano at the second trial, helped put Holgado in contact with other parents in a similar situation; people he could meet en route to Madrid. Two more volunteers, who worked for the “New Day” charity in Carmona, near Seville, set up a Facebook page for Holgado’s project, and coordinated with their contacts in town halls throughout Spain, so that he would be met by someone in each place he stopped.

On 28 September, at the roundabout by the petrol station where Juan had died, Holgado began his walk north – through Seville, Córdoba and Toledo, on his way to the capital. On the road, he was followed intermittently by wellwishers, local politicians from the towns he passed through, and photographers from La Voz del Sur, El País and Interviú magazine. On Facebook some 30,000 people followed his progress, receiving daily updates on his page, Support Father Courage. “The whole event was typical of Francisco, exaggerated and over the top,” Antonia told me. “It was too much about him.”

In mid-October, Holgado sat down in a room in the ministry of justice in Madrid with his lawyer and the minister, Rafael Catalá. Catalá was sympathetic to the old man’s pleas and told him that although he could not keep the case open indefinitely, he would promise to have it looked over. Five days before its legal expiry, the investigation was passed from the national police to the Guardia Civil, Spain’s oldest law enforcement agency, which, although organised as a military force, performs police duties.

Within days, there was an apparent breakthrough: a fingerprint on the blood-stained juice carton found on the scene, which had previously been discarded as evidence because it didn’t match the criteria for testing at the time, was matched to Agustín Morales, a well-known drug addict and serial offender, who, at the time of the murder, had lived near the petrol station. But it emerged that Morales had died in prison in 2006.

The court’s last roll of the dice came in June 2016, when it ordered that the 22 remaining fingerprints and DNA samples from Juan’s clothes be analysed again. The prints, although included in the original investigation, had not all been checked against an international criminal database of the 190 member countries of Interpol. In this same order, the judge also requested that Juan Holgado’s clothes be examined for traces of blood and DNA, and that a separate trace of DNA found on a shard of glass at the crime scene also be re-examined.

The Holgados knew this was their last chance to make any headway in their son’s case, but any optimism they may have felt was seasoned by 20 years of suffering and disappointment.

Towards the end of 2016, the Holgados learned that none of the court’s new inquiries had created a breakthrough. Of the 22 fingerprints, 11 were too indistinct to be analysed, and the rest did not correspond to anyone on the Interpol database. Moreover, the court found that Juan’s clothes had been destroyed 10 years earlier by judicial order, and the DNA revealed no positive match. The local press once again announced that the crime at the petrol station was closed.

One evening earlier this year, Holgado stood over his son’s headstone, his face scrunched into a frown. The springtime light shone through the clouds, illuminating the polished marble grave. His health was failing, but he said he would walk from Jerez to the European court of human rights in Strasbourg if he had to. “There has to be another way,” he said, “and I’ll find it.”

These days, he is no longer sure if Asencio, who has been in and out of prison over the past decade, or the other three original suspects, were even at the petrol station that night in 1995. For Holgado, this was not about justifying his past actions or proving that he had been right all along. “It’s about justice for my son, and I won’t stop until I have it,” he said.

Facebook Twitter Pinterest Francisco Holdago at a memorial to his son Juan in Jerez. Photograph: Aitor Alcalde

Bozie Hernandez, a friend of Holgado, said: “I have told him that after all he has done he deserves to rest.” But giving up the pursuit that has lent shape and meaning to his life for so long may not be possible. Holgado has told his tale so many times, and read it back to himself in so many papers, that it has become not just part of him, but perhaps all that is left of him. “I remember my old, normal life as if it were someone else’s,” he told me. The old Francisco, he believed, had died with Juan. “He has lived with Juan’s story for so long, I’m not sure he’d know what to do without it,” Cosano, his former lawyer, told me.

As the evening light faded, Holgado cleaned Juan’s tombstone and straightened the insignia of FC Barcelona, Juan’s favourite team, that hangs from the corner of the headstone. He could only stay for a while; he knew Antonia, who also visits almost every day, would be coming soon. Hope for justice is the only thing the couple now shares.

Holgado kissed his son’s grave and crossed himself before turning and walking to the cemetery gates. There, he said goodbye to the guard, collected his bike, and cycled the 6km from the cemetery to his home.

At his house, on a quiet street with few cars and a chapel at one end, he prepared a small meal in his cramped kitchen. He went to bed at 11 pm. Alone, on his lumpy mattress, he thought of death – not his own, but his son’s. Like he does most nights, he imagined his boy’s pain, his last thoughts and last sights, and he wondered if the story that he has lived for 21 years will ever end.

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• This article was amended on 2 October 2017. A photo caption on an earlier version said Antonia Castro was the father of Juan Holgado. This has been corrected to mother.

