Once the murder capital of the world, the Colombian city of Medellin, has been transformed into an attractive and vibrant city. But on the outskirts there is a dump where people say the truth lies buried - the bodies of dozens of people who were "disappeared" in years of bloody civil conflict.

Margarita Selene Restrepo stares out over the corrugated roofs of Comuna 13 - one of Medellin's poorest and most violent districts. From here, a few steps from her home, she can see a huge, deforested, earthen scar on the hillside opposite. In Spanish it is known as la escombrera - the dump. And Margarita can just make out areas recently fenced off with flimsy green plastic.

"Every day when I look across there it causes me such a lot of sadness. If she's there, she's so close. Yet at the same time, she's so far away."

Margarita is talking about her daughter, Carol Vanesa Restrepo. She was 17 when she disappeared in October 2002, and her mother believes her remains are buried in a disused part of the tip. She hopes that one day soon they will be exhumed.

And she is vigilant - every day she checks to make sure no more waste is deposited anywhere near the green cordons.

For many years, Comuna 13 was under the sway of left-wing guerrilla groups. The state had little influence here, but Operation Orion - launched just before Carol Vanesa disappeared - would change that.

They came in indiscriminately on the pretext of getting rid of the guerrillas Jeihhco

"The state decided it had to take back control of Comuna 13," says Jenny Pearce, professor of Latin American politics at the University of Bradford.

"But the way they did it seems to have been in alliance with paramilitary groups. And the paramilitaries subsequently went in and 'disappeared' at least 200-300 people from the area. So the bodies at la escombrera are the victims of what can only be called a state crime."

Locals remember the operation and its aftermath as a period of "absolute terror".

"There were more than 1,000 men from the state's forces, two helicopters and more than 800 paramilitaries," says Jeihhco, the founder of a cultural centre in Comuna 13. "They came in indiscriminately on the pretext of getting rid of the guerrillas."

When the army withdrew after four days, the paramilitaries became the new lords and masters of Comuna 13. Carol Vanesa Restrepo and two of her friends have not been seen since.

Families of the disappeared - women like Margarita - have been calling for la escombrera to be excavated for more than a decade. Now the city's government has begun technical assessments of part of the site identified by a former paramilitary commander, known by his alias, Movil 8.

"He grew up in Comuna 13, so he knew the area well and was able to identify places he thought bodies had been dumped by using landmarks like trees and electricity pylons," says Jorge Mejia Martinez of the Medellin mayor's office, who is overseeing plans to excavate the site.

Image caption Excavating the site is complicated and parts of the dump are still used for construction waste

There is uncertainty about the number of people buried beneath the tons of earth and rubble collected from building sites and dumped here. It is believed some were discarded here before the killings in 2002, and that the paramilitaries were not the only perpetrators.

Find out more Listen to Linda Pressly's report on Assignment on BBC World Service on Thursday 1 January or catch up later on iPlayer

"The story began much earlier with the left-wing guerrillas," says Martinez.

"Other criminal groups have been active too, and bodies may have been brought from other parts of the city, and even from the wider region."

Some even believe the disposal of human remains is still continuing.

Medellin became the most murderous city on the planet in the days of Pablo Escobar - the man who industrialised the processing and export of cocaine in the 1970s.

But Escobar's Medellin Cartel didn't disappear when he died in a police shootout in 1993. It mutated. Its associates - and their successors - became paramilitaries who fought guerrillas and continued trafficking drugs. They also reinforced existing criminal organisations. And they formed new ones.

Image caption Graffiti criticising the military and paramilitary operations in Comuna 13 is common

Though Medellin's homicide rate is at one of its lowest points for three decades, the number of forced disappearances has increased, says Fernando Quijano, director of Corpades, an institute that monitors violence in the city.

To a visitor, though, Medellin now feels very safe. The transport system includes a state-of-the-art metro system, and cable cars. There are tech hubs, museums, dozens of new schools, and also library parks. Comuna 13 is home to the Parque Biblioteca San Javier - a vast, airy multi-level, multi-purpose building. It is a place for study, cultural events, and education - a meeting point for the community.

The transformation of the city has been called the "Medellin Miracle", and there is much pride at what has been achieved. At the heart of the urban philosophy is the aim of including the excluded, a desire to bring governance to districts like Comuna 13, and connect people to the city.

Image caption Cable cars now connect hilly areas of Medellin that used to be hard to get to

Image copyright AFP Image caption Covered escalators also make the hilltops of Comuna 13 easier to reach

"People come to Medellin to see those buildings that we defined and created," says Sergio Fajardo, who was mayor of the city when it underwent much of this transformation, and is now governor of the larger Antioquia region.

"Those buildings gave our people hope that things could happen, that elegant things could happen, and that the most beautiful places could be where they lived. That's a message of dignity, and it's powerful."

Image copyright AFP Image caption The Parque Biblioteca San Javier is one of the new developments

Yet, despite these improvements, la escombrera with its secrets still concealed, looms over Medellin. And, as Fajardo says, there are "many escrombreras" throughout Colombia.

Over nearly six decades, almost a quarter of a million people have been killed in the country's civil conflict - the majority of them civilians. In Medellin, numerous people have a story of violence and loss.

At the city's Parque de la Vida ("park of life") building, part of the University of Antioquia, a group of women have gathered weekly for the last seven years. They meet and they sew. The women make dolls. And each of the figures represents a loved-one killed or disappeared.

Maria Lucely Durango has stitched her son, a 17-year-old murdered in 2011 when he crossed the invisible line in his neighbourhood that marked rival gang territory. She has dressed Juan Felipe Henao Durango in a graduation gown - the representation of a son who would never fulfil his promise.

Joining the sewing circle has been valuable therapy for the women, and helped them accept their bereavements. Often their stories are a demonstration of how cruelly indiscriminate the violence of Colombia's civil conflict has been: one mother lost a son to left-wing guerrillas, and a son and a daughter to the paramilitaries - the armed groups acting in opposition to those guerrillas. But most of the women who attend the group lost their loved-ones in paramilitary operations.

Image caption Maria Lucely Durango with a doll of her son Juan Felipe Henao Durango Image caption Women whose relatives have disappeared have made dolls of about 150 people - all presumed dead Image caption Teresa Rendon's husband disappeared at the age of 53 - she has been a widow for two decades and says she has had to walk a long and hard road to survive Image caption Teresa also lost her son, a taxi driver who was pulled out of his car by two armed men at traffic lights - she is still waiting for "truth, justice and reparation" Image caption Rosalba de Jesus Usma's daughter and two sons disappeared - Libia and Adrian were killed by paramilitaries, and Duber by guerrillas Image caption The label on Adrian's doll explains how he was taken from his home one evening and that 18 months later his abductors called to say they had killed him Image caption Maria Gloria Holguin's son Carlos Emilio Torres Holguin died in the aftermath of Operation Orion and she suspects he is buried in la escombrera previous slide next slide

So will the families of the disappeared of la escombrera see their loved-ones disinterred? Three areas for excavation have so far been identified by Movil 8.

"In areas one and two, we're recommending that the excavation goes ahead," says the engineer who has been assessing the site, Gabriel Jaime Cardon Londono.

"In area three, we don't think it would be safe because it would mean digging down a lot deeper - about 25m. Any kind of movement of the earth here would be much more dangerous."

There are not only physical challenges. The cost could be prohibitive - $4m or $5m according to an estimate made in 2010.

"We hope it will be possible to reduce that figure," says Jorge Mejia Martinez. "But whatever the cost, the decision of the mayor's office is to unearth the truth that is hidden here."

Image caption The stone reads: To the victims of forced disappearance of Comuna 13 of Medellin at the hands of the Bloque Cacique Nutibara [paramilitaries]. So we don't forget them.

For Jenny Pearce la escombrera is illustrative of how Colombia has experienced violence over many decades.

"It's emblematic of impunity, of the lack of a rule of law that says to people you can't murder someone, throw them on to a rubbish tip and get away with it. La escombrera shows the layers and layers of violence from all armed groups going back decades. There are people who want to show the city's overcome its worst decades - of course, Medellin wants to move on. But until the past is addressed, and there's security that people can trust, that's difficult."

Margarita Selene Restrepo lives at one of the highest points of Comuna 13. It is a very steep climb. But it has been made easier in part by another Medellin innovation - an escalator that has replaced 350 of the steps that rise almost vertically. Now, that part of the journey to Margarita's home takes just four minutes, compared to the hour it might have taken before. She is not impressed. For Margarita, investment in the city's infrastructure highlights the lack of commitment to victims like her.

"If the government cared about us, they would have done something about la escombrera," she says.

If the exhumation goes ahead, there is at least a chance Margarita will find out what happened to her daughter that day in October 2002.

Listen to Linda Pressly's report on Assignment on BBC World Service on Thursday 1 January or catch up later on iPlayer

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