On a dusky evening last spring, Jorge Alberto Martinez Chavez was tossed into the hell that is El Salvador’s prison system: a holding cell barely bigger than the bed of a pickup, where more than 50 prisoners were crammed together, some on the sweat-soaked floor and others spilling out of thin hammocks crisscrossed from ground to ceiling.

The air was hot and humid, and prisoners’ half-naked bodies reeked of urine and ulcers from a recent outbreak of bacteria, according to a guard. A few weeks later, Martínez Chavez collapsed, foaming at the mouth. He was the fifth inmate from that cell to die in four months.

He never should have been there in the first place. Police, prosecutors and a judge mistook him for a different Jorge Alberto Martinez Chavez, a man eight years younger with a gang tattoo across his chest and a criminal history that includes charges of extortion, illegal gun possession, and murder.

Martinez Chavez’s death exposes deep flaws in El Salvador’s justice system, with implications that go well beyond this tiny nation of six million. At a time when thousands of Central Americans are fleeing towards the United States, and border control is at the top of President Donald Trump’s agenda, the weaknesses of this region’s courts and cops have assumed outsize importance. The same institutions that allowed an innocent man to die have failed to prevent street gangs from turning the country into one of the most violent in the hemisphere.

The US government has spent hundreds of millions of dollars in recent years to help Central American countries capture and prosecute gang leaders and corrupt officials. Although there have been some advances, the system remains dysfunctional. Police in El Salvador frequently don’t use forensic evidence, prosecutors handle several hundred cases at once, and prisons are so bad that the Supreme Court has ruled them unconstitutional.

The combination of these failings – during a crackdown in the streets and a lockdown in the prisons – was fatal for Martinez Chavez, 37, a bus dispatcher, volunteer first-responder and father of two with little in common with the fugitive authorities sought.

Gangs use the prison system as a rent-free corporate office, directing murders and extortion rings with sneaked-in phones (Getty)

“His only sin was having the same name,” said public defender Saul Sanchez.

The crime that would land Martínez in jail occurred in October 2014 in San Pedro Masahuat, a town with cobblestone streets in the La Paz region, an hour southeast of San Salvador. Five men with guns ambushed a sixth man, who ducked behind cars to avoid the bullets. He survived, and later described his assailants to prosecutor Guillermo Molina: four low-level gang members and a leader called “Wisper”.

The victim knew Wisper’s name: Jorge Chavez. He had an idea where he lived – a sheet-metal shack on the edge of town – and his age: about 26. Chavez was covered in gang tattoos, including “MS” (for “Mara Salvatrucha”) across his chest and an eagle on his back.

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The prosecutor’s investigation was based almost entirely on the victim’s testimony. This is common in El Salvador. Despite US-led efforts to introduce scientific evidence to the judicial system – starting during El Salvador’s 1980-1992 civil war and continuing with the current Alliance for Prosperity aid package, which includes a $4m (£3.2m) forensic training programme – reform has been sluggish, according to legal scholars and watchdog groups.

“The legal system was created to serve the oligarchy, and continues to favour the rich and powerful,” said anthropologist Juan Jose Martinez. These days, corrupt business executives and politicians often escape scrutiny while gang violence overwhelms police and prosecutors.

Authorities in San Pedro Masahuat caught the four lower-level gang members but couldn’t find the notorious Wisper. They photographed his house, but according to the case file, didn’t do much else to locate him.

Police suspect Jorge Alberto Martinez Chavez was poisoned (Getty)

Prosecutors needed more details, so they consulted a federal database of citizens and learned of a 37-year-old man named Jorge Alberto Martinez Chavez. A week later, on 17 December, prosecutors checked online prison records and found another, 29-year-old man with the same name.

The differences between the two men were sweeping: not only were they eight years apart, but they hailed from different towns. The younger man was a Mara Salvatrucha gang member who had been imprisoned for extortion in 2010, and was wanted in connection with several slayings. He went by Jorge Chavez – the same name offered by the victim.

The older man was known as Jorge Martinez. He had no criminal record.

Despite the disparities, prosecutors filed charges against 37-year-old Jorge Martinez. Molina said the witness identified Martinez Chavez in a photo lineup. However, the same witness later identified the other man, Jorge Chavez, in another photo reel.

This was the start of the chain that ended in Martinez Chavez’s death.

In early 2015, Wisper was accused of killing two young men in San Pedro Masahuat. After a series of blunders, these charges, too, would end up following the other Jorge Alberto Martinez Chavez to the grave.

Until 25 April 2016, he had no idea about any of this.

That day, a typical scorcher in San Salvador, capital police stopped Martinez Chavez at the gas station where he worked dispatching buses; they later said he had looked suspicious. They ran his name through a database and couldn’t believe their luck. They thought they had stumbled upon Wisper, a gang leader and one of the 100 most sought-after criminals in the country, and promptly detained him.

Although Martinez Chavez was arrested on a single, erroneous warrant, when Judge Daniel Ortiz in San Pedro Masahuat received news that “Wisper” had been captured, he tacked on the double murder. He didn’t notice the discrepancies with the description of that suspect.

“We judges aren’t investigators,” Ortiz said. He never saw Martinez Chavez in person but sent him to jail anyway. With heavy caseloads, judges often don’t see prisoners until they have spent weeks or months locked up – in Martinez’s case, in a disease-ridden, gang-controlled police holding cell in the nearby town of San Juan Talpa.

Martinez Chavez kept insisting he was innocent. He swore to his public defender, Sanchez, that he was not a gang member, stripping off his shirt to show he had no tattoos. His job as a bus dispatcher required him to travel through territory dominated by the 18th Street gang, which would have been impossible if he were a Mara Salvatrucha member.

Everything might have been settled by a police lineup, in which the victim would have to identify Martinez Chavez as the man who tried to kill him. That was postponed twice, first on 16 May because the judge called in sick, and then on 23 May because the prosecutor’s office forgot to arrange transportation for the victim.

And then time ran out. Martinez Chavez, who had spent a month in jail without ever seeing a judge, died on 25 May in a San Salvador hospital.

At least 25 inmates died in Salvadoran police holding cells between January and June 2016 (Getty)

On 11 July, Judge Ortiz archived the attempted murder case, citing a police report that “Wisper” had died.

When Martinez Chavez arrived in San Juan Talpa in late April, the holding cells built for 20 people housed more than 110. The jail had become a petri dish for outbreaks of scabies, pneumonia and tuberculosis. In one instance, after 50 sick inmates were quarantined with an unidentified virus, police scrubbed the cells with bleach. Then the inmates were moved right back in.

In April, two prisoners died in the cell in the span of 48 hours. A police officer told the daily newspaper La Prensa Grafica that inmates attributed the deaths to ghosts. But the officer also said prisoners shouted and threw each other against the walls.

Investigators from the national human rights office suspect the men were beaten to death by their fellow prisoners. One was covered in bruises; the other had deep scars on his wrists and ankles. They were among at least 25 inmates who died in Salvadoran police holding cells between January and June 2016. Ninety-six more died in the same period in prisons, hospitals, and transport vehicles; nearly one-third were murdered, and the rest died of illness or suicide.

According to the Institute for Criminal Policy Research, El Salvador’s prisons are the most jam-packed in the Western Hemisphere except for Haiti’s. The populations began to swell in the mid-2000s as a result of President Francisco Francisco Flores Perez’s “Strong Hand” policy, a series of tough-on-crime measures that included increased police raids and longer sentences. Now a prison system built for 10,000 inmates houses more than 37,000, not including about 5,000 held in police jails.

“The ‘Strong Hand’ policy didn’t consider what would happen when all these people got locked up,” said Rodil Hernandez, the national prisons director. Gangs are using the prison system as a rent-free corporate office, directing murders and extortion rings with phones sneaked in by guards and visitors.

Last March, Hernandez declared a state of emergency in seven prisons. Since then, thousands of prisoners have been barred from visits with relatives, doctors and judges. Human rights advocates have documented a spike in tuberculosis and other contagious diseases. “We found prisoners who were literally rotting,” said Gerardo Alegría of the human rights office, describing oozing ulcers, infected gunshot wounds and limbs that needed to be amputated.

Judicial processes have ground to a halt, and the total prison population has increased 10 per cent in the past six months, sending the government scrambling to build new penitentiaries. On 9 February, legislators extended the lockdown until 2018, crediting it for a 20 per cent drop in killings over the past year.

El Salvador’s Supreme Court found in an investigation that prisoners have as little as three square feet of space, lack adequate food, water and medical care, and could spend months or years locked up without trial.

Despite the diseases and the violence, Martinez Chavez seemed fine when his father went to the jail on 19 May. Family members dropping off food can catch a glimpse of inmates through the iron bars of the police station door.

Four days later, just hours after the cancelled police lineup, Martinez Chavez collapsed and was taken to a hospital. He died on 25 May.

The police report listed “suspected tuberculosis” as the cause of death. The autopsy reported pneumonia, although it found that Martinez Chavez had a burst liver. Autopsies in El Salvador are often unreliable, according to international forensic experts; coroners may perform half a dozen on a single shift.

Police at the San Juan Talpa holding cell suspect Martinez Chavez was poisoned. Imprisoned gang members sometimes kill non-gang cellmates as a way to ensure they don’t tattle once they leave jail.

The human rights office is investigating how Martinez Chavez died and why he was arrested in the first place.

In an interview, Judge Ortiz said he only realised after Martinez Chavez died that there were two men named Jorge Alberto Martinez Chavez. “They had almost the exact same characteristics,” he said.

Deputy Commissioner of Police Jose Luis Mancia claims officers acted correctly in detaining Martinez Chavez, because there was a warrant for his arrest. The address on the warrant, however, belongs to the other man. Wisper is still at large.

Martinez Chavez’s widow, Maritza Garcia, struggles to support two sons on the $15 to $25 a week she makes cleaning a school. Jorge Martinez Sr doesn’t expect to learn the truth from the investigation into his son’s death.

“A better use of time would be to investigate the cases of all the innocent people imprisoned who are still alive,” he said.

Last fall, three more prisoners died in the San Juan Talpa holding cell.