As peace appears to be in sight, Channel 4 News goes in search of what could prove the largest mass grave in Colombia, a country where 220,00 people have been killed over the last half century.

Manuel Santos, president of Colombia, Raul Castro, President of Cuba and Rodrigo Londoño, known as ‘Timoshenko’, the leader of FARC , shake hands

In a bland Havana conference room, writes Thom Walker, Cuba’s President Raul Castro stood between his Colombian counterpart and the leader of Latin America’s longest running armed insurgency, and pressed their hands together.

President Juan Manuel Santos and the head of the Revolutionary Armed Forces of Colombia, (FARC) Rodrigo Londoño, known as Timoshenko, both dressed in symbolically crisp white shirts, could just about muster a smile as the cameras clicked feverishly around them.

Three long years of negotiations, two great adversaries, and one fragile peace deal.

Around 220,000 people have been killed. 20,000 people are still missing and five million have been internally displaced, more even than war-torn Syria.

For the country and the entire region, it could be the beginning of the end of almost half a century of war.

Both sides have agreed to create special tribunals with international judges to prosecute crimes related to the conflict. Covering both state actors and FARC members, it could relate to around 15,000 people. A sixth month timetable has been drawn up for a more comprehensive deal, with the FARC agreeing to lay down their weapons shortly after.

If you step away from the headlines however, peace in Colombia will require much more than a bipartisan deal. This is not a conflict between two sides, but many. For decades, Colombia has been the world’s largest producer of cocaine. The subsequent battles for control of this multi-billion dollar industry have created a culture of violence so pervasive that few see a paper agreement carrying much weight.

Different guerilla groups, state-sponsored paramilitary forces and urban gangs, all of whom, like the FARC, are involved in drug trafficking, remain heavily armed and active. It seems unlikely they will be willing to relinquish what control they have without a fight.

We recently spent a week in Medellin, the former kingdom of the world’s most notorious drug lord Pablo Escobar. Colombia’s second city once boasted the world’s highest murder rate.

There, we met up with forensic anthropologist John Freddy Santana, who knows the human cost of the war better than anyone. He has spent his life looking for the thousands of people who are still missing. Now his latest project is to unearth the largest urban mass grave in the world, where there may be as many as 500 bodies buried.

It’s known as the ‘Escombrera’ or dump, and sits on a verdant hillside looming over Medellin like an open wound.

As John Freddy showed us round the site, we were joined by several women. All of them were looking for loved ones.

Margarita Restrepo hasn’t seen her daughter Carol Vanessa in 13 years. She was just 17 when she disappeared.

Looking out across the Escombrera she told us: “they’re forgotten tombs, it’s a forgotten mass grave, as if they had no loved ones, or family. Where is she? What is she doing? How is she doing? Is she alive? Is she ok? Did they kill her? Did they torture her? It’s so hard. There are no words to describe it.”

Seven of John Freddy’s co-workers have disappeared in recent years. Not everyone is happy for him to dig into Colombia’s past. He also lost cousin more than a decade ago. Her body has never been found.

“This is the phenomenon of disappearances,” he said. “It’s like the perfect crime. What are they going to accuse you of? Of murder, with no body? No. Of disappearing someone? No. Did you see me dragging a body?”

It was only when we went to meet two men at the heart of this ongoing conflict that we realised how elusive Colombia’s peace remains.

In their run-down neighbourhood, they are the de-facto kings, selling drugs and policing who comes in and not. We met at night, in a safe house, and they only spoke to us on strict condition we didn’t reveal their identity.

They rubbished the peace process. “It’s a farce, just government manipulation,” one scoffed.

We asked them about Colombia’s new image, as a country safe for tourists. Was it now free from the endemic violence of the past?

“Now, when we have to kill someone, we take them somewhere and chop them up into pieces, and throw them in the river. So there’s no evidence.”

Growing up in their neighbourhood, they said they had few options; it was either join the gang and fight, or die yourself.

It was late, and we couldn’t be sure who might suddenly burst in.

As we left, one of them turned to us with a shrug: “This war will never end. This war will always be there because drug trafficking always brings war. It’s a vicious circle, with no end.”