It is 20 years since the Srebrenica massacre, Europe's worst atrocity since World War Two. In July 1995, Bosnian Serb forces killed more than 8,000 Muslim men and boys in the eastern Bosnian enclave of Srebrenica, a designated United Nations "safe haven". About 15,000 men and boys managed to escape and fled through the woods, but many were murdered by the Serbian army who ambushed them, disguised as UN soldiers.

War had broken out in Bosnia in April 1992. The Bosnian Serb army swept eastwards. Srebrenica, a town of 36,000 where Muslims made up 75 percent of the population, was taken over by Serb troops but Muslims regained it after several weeks.

Early in 1993, Serbs started an offensive on Muslim-held areas. Srebrenica and Zepa became isolated enclaves deep in Serb-held territory. Muslims from the area flocked to Srebrenica and the population swelled to 60,000. They had little food, water or medical supplies.

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31 March 1993: Bosnian Muslim refugees are transported on a United Nations truck in a convoy as they flee the Serb-besieged enclave of Srebrenica for TuzlaPascal Guyot/AFP
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31 March 1993: Muslim women and children eat snow in order to quench their thirst as they are evacuated from SrebrenicaReuters

In April, Srebrenica, Zepa and Gorazde in eastern Bosnia were declared three of six UN "safe areas". The United Nations Protection Force deployed troops and the Serb attacks stopped. But the town remained isolated and only a few humanitarian convoys reached it in the following two years.

Then Bosnian Serb President Radovan Karadzic ordered that Srebrenica and Zepa be entirely cut off and aid convoys be stopped from reaching the towns.

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5 August 1993: Ratko Mladic, Bosnian Serb military commander, whispers into the ear of Radovan Karadzic, leader of the Serb-run part of BosniaAFP
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31 May 1993: Heavily-armed Bosnian Serb soldiers patrol through a field near the town of SrebrenicaReuters
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28 February 1994: Dutch soldiers accompany a UN convoy of armoured vehicles on their way to Lukavac and SrebrenicaAFP

On 9 July 1995, Karadzic issued a new order to conquer Srebrenica. Troops surrounded the enclave and attacked the observation posts of Dutch peacekeepers, taking about 30 soldiers hostage.

The following day, Serbian forces started shelling Srebrenica. The Dutch threatened the Serbs with Nato air strikes if they did not withdraw by morning.

Another day later, Nato planes bombed Serb tanks outside Srebrenica. The Serbs threatened to resume shelling and kill the captured Dutch soldiers. Air strikes stopped and in the evening of 11 July, Bosnian Serb commander General Ratko Mladic entered Srebrenica.

An estimated 30,000 Muslim refugees packed around the Dutch peacekeeping base in Potocari, just north of Srebrenica, after Bosnian Serb forces seized the "safe area". Mladic sought to calm them, telling the crowd they did not have to be afraid.

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12 July 1995: Bosnian Serb army Commander General Ratko Mladic hands out drinks to Bosnian Muslim refugees from Srebrenica, as they wait to be transported from Potocari to KladanjReuters
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12 July 1995: A Bosnian Muslim man helps his elderly cousin as they wait to be transported from Potocari to KladanjReuters
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13 July 1995: A Bosnian Serb soldier fires a machine gun during a mopping-up operation near SrebrenicaReuters
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13 July 1995: Bosnian Serb commander Ratko Mladic shakes hands with one of his soldiers in Srebenica after they took control of the townReuters

Bosnian Serb forces put the frightened refugees on to buses to leave. Many of the refugees were evacuated to Kladanj, 50km (30 miles) away on the edge of government-held territory.

The UN noticed that most of the refugees arriving from Srebrenica were women, children, and the elderly, and became concerned about the fate of the men.

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12 July 1995: Bosnian Muslim women and children wait for transportation from Potocari to KladanjReuters
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14 July 1995: Thousands of refugees from Srebrenica board buses at a camp outside the UN base at Tuzla AirportReuters
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13 July 1995: Bosnian Muslim refugees from Srebrenica are transported by the UN from Potocari to KladanjReuters
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14 July 1995: Bosnian women and children, refugees from Srebrenica, mourn their missing men in the refugee camp at Tuzla AirportReuters

Over the week that followed the fall of Srebrenica, a total of about 8,000 men and boys from the enclave are estimated to have been killed by Bosnian Serb forces in detention or while trying to flee through the woods.

Men were crammed into warehouses, schools and barns in the area outside Srebrenica.They were shot and buried in mass graves.

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Video footage shows members of a paramilitary group called the Scorpions taking six emaciated young men out of a truck with their hands tied behind their backs. They are led to a clearing where four are seen being shot at close rangeHague Tribunal/Reuters
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Bullet holes pepper a wall where Bosnian Muslims were executed at an agricultural cooperative in Kravica near BratunacDado Ruvic/Reuters
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18 September 1996: Forensic experts investigate bodies, many of them blindfolded and with their hands tied around their backs, in a mass grave outside the village of PilicaOdd Andersen/AFP
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24 July 1996: The bodies of Muslims killed during the exodus from Srebrenica are seen in a grave near the eastern Bosnian village of Nova KasabaReuters
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28 March 1997: Stacks of unidentified corpses found in mass graves line the walls of an underground shelter at a morgue in TuzlaReuters

Identification of the bodies is difficult: bodies were broken up by excavators that bulldozed them into mass graves. Bodies were also moved from the original graves to secondary locations to conceal the crime.

Forensic experts painstakingly work through what is left of the bodies found in the hundreds of mass graves that have been discovered in the area.

Every year on 11 July, the remains of those who have been identified over the past year are buried at the Memorial Centre in Potocari.

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10 July 2001: A forensic expert works in a morgue in Tuzla containing the remains of more than 3,500 Bosnian Muslim victims of the 1995 Srebrenica massacreReuters
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8 June 2005: Forensic experts sort through bones and body parts found in a mass grave in the village of LipljeReuters
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7 July 2005: A forensic expert with the International Commission on Missing Persons holds a photograph found on the remains of a victim of the 1995 Srebrenica massacreDamir Sagolj/Reuters
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7 July 2005: Personal items found in a mass grave are laid out for identification at the office of the International Commission on Missing Persons in TuzlaDamir Sagolj/Reuters
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9 July 2005: A Bosnian Muslim woman looks through the window of a car as she waits for 610 coffins containing the remains of victims of the Srebrenica massacre to arrive in PotocariDamir Sagolj/Reuters
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9 July 2005: Men search for their relatives among coffins containing the remains of 610 Bosnian Muslims due to be laid to rest in a memorial cemetery in PotocariJoe Klamar/AFP
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11 July 2005: Thousands attend the burial ceremony of 610 Bosnian Muslims at the memorial cemetery in Potocari on the 10th anniversary of the massacreJoe Klamar/AFP
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11 July 2005: Bosnian Muslim women cry as their relative is buried in PotocariDamir Sagolj/Reuters

After the war, Karadzic went on the run and remained a fugitive for 13 years until he was arrested in Belgrade in 2008. He had evaded the authorities by working as an alternative medicine practitioner in a private clinic under the false name of Dragan David Dabic.

Mladic managed to evade justice with the help of Serbian army comrades and the Serbian state. He was finally arrested in 2011 after the election of reformist president Boris Tadic. Both Karadzic and Mladic are still standing trial at the United Nations war crimes tribunal in The Hague.

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Bosnian Serb wartime leader is pictured in 2008 and in 1995. The fugitive was arrested in a suburb of Belgrade where he lived posing as a doctor of alternative medicine, sporting long hair, a beard and glassesReuters
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Bosnian Serb wartime general Ratko Mladic in seen after his arrest in 2011Reuters

Twenty years on, the forests and farmland around Srebrenica are still yielding bones, but more than 1,000 victims have yet to be found.

Bodies were tossed into pits then dug up months later and scattered in smaller graves by Bosnian Serb forces trying to conceal the crime. Investigators believe at least one more big grave still eludes them.

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1 July 2015: Top row: Curana Zukanovic and a photo of her sons Jusa and Hajrudin, who are still missing 20 years after the massacre. "I pray to dear Allah every day and hope not to die without finding my children," she says. Bottom row: Nura Sulic and a photo of her son Mirsad, also still missing. She says: "His photograph is all I have left of him. I pray to dear Allah to find at least one, smallest bone. Anything. So that we would both finally be at peace."Dado Ruvic/Reuters