Even in his dreams Vladimir Vukcevic cannot forget Ratko Mladic. The Serbian war crimes prosecutor sees the former Bosnian Serb commander standing in a Yugoslav Army base. The imagined Mladic is taller and younger than the real one. But his freedom taunts ­Vukcevic in his dream, just as it does in his waking life.

The prosecutor has been coordinating the hunt in Serbia for Mladic since 2006. It is his job to ensure that Mladic is ­arrested and sent to the International ­Criminal Tribunal for the former ­Yugoslavia (ICTY) in The Hague, where he is charged with war crimes, crimes against humanity and genocide.

A psychologist would doubtless interpret Mladic’s tall and youthful dream figure as symbolising a more difficult adversary than Vukcevic had expected. “I thought this job would be finished in three or four years, but I was wrong,” he says. Grey-haired, neatly barbered with a trim beard and moustache, even at 60, Vukcevic retains a youthful vigour.

Mladic is accused of the worst atrocity in Europe since 1945. In the days after the Bosnian Serb army captured Srebrenica in July 1995, soldiers under his command massacred up to 8,000 Bosnian Muslim men and boys. The eastern Bosnian town was a UN-declared “Safe Area”, with a garrison of Dutch peacekeepers. They failed to stop the enclave being overrun, failed to protect the male civilians and even forced out those who had taken refuge inside their base.

“We made a psychological profile of Mladic. He is a soldier and not prone to corruption. He took care of his men and in that respect he was a positive person,” says Vukcevic. “But his behaviour after the capture of Srebrenica was pathological. When you see how he treated the other side, saying that the Serbs have conquered the Turks and can take revenge on the Balija [a derogatory term for Bosnian Muslims], I think that was a direct incitement to a massacre and we know the ­massacre happened just after. Mladic was convincing the women and children that nothing was going to happen to them, and was giving out chocolates to the children, throwing them, as if to the dogs. There is footage of him patting the head of a frightened boy of 12 or 13. He was also killed.”

In May, Mladic’s family asked a Belgrade court to declare that he was dead, and so bring closure. The request was denied. Senior European officials have told monocle that the working assumption is Mladic is alive and is probably in Serbia or its border regions. Three separate agencies are working on the search: the Serbian intelligence service (BIA), the country’s military intelligence and the police. Western intelligence agencies are also helping. Vukcevic won’t say which ones, but the CIA and Britain’s MI6 seem to be the lead candidates.

After the arrest of former Bosnian Serb president Radovan Karadzic in Belgrade in July 2008, many expected Mladic to be apprehended, along with Goran Hadzic, a former political leader of the Serbs in Croatia, who is also on the run. Karadzic had grown a beard, and was working, bizarrely, as an alternative healer. But as a military man Mladic understands secrecy, coded communications and other covert skills needed for a life as a fugitive.

Western officials say that under Sasa Vukadinovic, director of the BIA since 2008, the service is focused on finding Mladic. But during Slobodan Milosevic’s reign, the security service was a virtual state within a state. Jovica Stanisic, its chief during the Yugoslav wars, is now on trial at the ICTY. Vukcevic says that since 2008 the BIA has been committed to finding Mladic, but before that there “were certain obstructions”. Still, these are new times in Serbia and the net is closing.

Zdravko Tolimir, one of Mladic’s deputies, was arrested in 2007 and is now on trial at The Hague, charged with genocide and war crimes at Srebrenica. In February, Serbian police again raided Mladic’s home in Belgrade. They found a false wall concealing his wartime notebooks, documents, computer memory sticks and sim cards. Vukcevic’s team have advantages not shared by their colleagues in The Hague, he says. “Our ­colleagues there realised very quickly that our capacities are much bigger than they thought. We helped them a lot, we know the local mentality, how to approach people and to talk to them, and they ­appreciate this.” Vukcevic’s office also prosecutes Serbian war criminals and, as of September, had sentenced 47 people to a total of 620 years in prison.

Investigators are focusing on the money and medical trails. Keeping someone fed, clothed and housed for years ­demands a complex financial network. Mladic is also believed to be suffering from medical problems, including the after-effects of a minor stroke, high blood pressure and kidney stones, all of which require medication. The Serbian prosecutor frequently sends him messages through the press. “I told him recently that generals don’t usually hide in a hole; that since he claims he is innocent the only place he can confirm that innocence is in court; that he is being selfish to his family; that he is a coward because he is hiding behind the whole Serbian people and the country is his hostage.”

Mladic was indicted in 1995, making it a legal obligation for any UN member state to arrest him and extradite him to the ICTY. For the first two years after the ­Bosnian war ended in 1995, his whereabouts were known to western intelligence agencies. He was living in a ­military base outside Sarajevo. His arrest, it was feared, would have torn apart the tentative post-war peace agreement. From there he moved back to Belgrade, where he lived openly, dining out and attending football matches, until the October 2000 revolution that brought down his protector, Milosevic.

Bojan Dimitrejevic, a former assistant minister of defence now working as a historian, would sometimes bump into Mladic in Belgrade’s Kosutnjak Park. “I walked with him three times. I said I was a historian and he reacted positively. I wanted to ask him so many questions.”

During encounters, Mladic was accompanied by his wife and a bodyguard, says Dimitrejevic. “He was bright, he remembered what we talked about, who I was and he was clearly commenting on events in detail. He refused a formal interview, saying it was not the time.” Dimitrejevic believes that after 2000, Mladic was advised to adopt a lower profile and was moved around Yugoslav Army facilities until 2002, when he probably returned to Belgrade. From there the trail turns cold.

Serbia is paying a high price for Mladic’s obduracy. The country has applied for membership of the European Union but cannot join until he is caught. It is a dark irony that Belgrade, once the most sophisticated and cosmopolitan city in eastern Europe, is now 20 years behind Budapest or Prague. The city still buzzes with Balkan joie de vivre, but the streets are grey and potholed. The fine old Habsburg buildings are crumbling.

Under the pro-western government of President Boris Tadic, which was formed in 2008, there is complete political will to capture Mladic, says Milica Delevic, head of the European Integration Office. “People in government see this as an obligation to the ICTY and the EU. But it is also an obligation to ourselves, to deal with the past and to ­confront it.” A senior European official agrees, telling Monocle: “The arrest of Karadzic removed any doubts about the government’s commitment.”

The Hague and Belgrade are different worlds. Belgrade’s ramshackle charm captivates; The Hague’s spotless streets and shiny kerbstones are crowded with prim matrons on bicycles. The ICTY is housed in a former insurance building in a tree-lined suburb. The courtrooms resemble a municipal council chamber and, except when a protected witness is testifying, are open to the public. Most days, there is little sense of drama. When Monocle visits, Zdravko Tolimir is on trial in courtroom No 3. It is hard to imagine this thin, balding man once strutting across the killing fields of Srebrenica. But perhaps that is his intention.

In a large corner office nearby, Serge Brammertz is coordinating the international effort to find Mladic. Brammertz has served as the ICTY’s prosecutor since 2008. A trim 48-year-old, he was previously based in Beirut, heading the UN ­investigation into the assassination of Lebanese prime minister Rafik Hariri. It is especially important that Mladic is caught this year, the 15th anniversary of the Srebrenica genocide, both for the victims and for justice, he says. But more than that, the credibility of international criminal justice is at stake.

“This tribunal was set up for the prosecution of people like Mladic,” says Brammertz. “If the international community is not capable of arresting him, it would be a negative legacy for the tribunal and a negative precedent for other tribunals and courts, because it would show that at a certain moment in time the political pressure eases.”

Brammertz reports to the UN Security Council every six months and is due to do so again in December. A positive report is crucial for Serbia’s EU accession. So far, the verdict is mixed. Serbia is cooperating but in June, Brammertz said its efforts so far had produced “few tangible results”. “Everyone is telling me the political will to find Mladic is there, so I have no reason to doubt that,” he says. “But if this is really top priority, you have to devote maximum resources and maximum energy, and as we said in our last report, this is not the case. Our hypothesis is that there are still influential people supporting him.”

Beyond the diplomatic negotiating in Brussels and New York, the glacial pace of the trials and the legal hair-splitting, is the human factor. This year Brammertz was invited to Srebrenica by the Mothers of Srebrenica, a victims’ support group. Many of these mothers and widows are now utterly alone, having lost their husbands, sons, brothers and cousins. Many lack even a grave to mourn at. After the massacre the bodies were buried in mass graves, and then dug up and reburied in an attempt to conceal what had happened. Even a single limb, once identified, gives a focus to their grief.

Brammertz was profoundly moved by his trip. “One woman I spoke to lost 42 members of her family. When you meet these women and ask them what you can do for them, the answer always is: arrest Mladic. That will not change their suffering. But it will at least give them a feeling of justice being done.”