The Hague: European authorities are seeking testimony from some of the hundreds of thousands of refugees fleeing Middle East violence as they try to build war crimes cases linked to the conflicts in Syria and Iraq.
As witnesses to atrocities, they are invaluable to prosecutors preparing trials in European courts that will offer a way round the United Nations impasse that has prevented the setting up of an international court for Syria.
The search for evidence takes a variety of forms. Dutch and German immigration services hand out leaflets to arriving migrants, inviting them to testify. In Norway, police screen arrivals` mobile phones for evidence of possible involvement in war crimes.
"Over the next five years you`ll see a lot of prosecutions," said Matevz Pezdirc of the European Union`s Genocide Network, a forum that brings together police and prosecutors twice a year in The Hague to swap information about war crimes.
Some alleged perpetrators may be European citizens who have joined Islamic State; others may be militants who have travelled to Europe from Syria or Iraq, blending in with the more than 1 million migrants and refugees who streamed into the continent last year.
"You may have lots of victims or witnesses in one place, but you can`t move with a prosecution until you have a perpetrator in your jurisdiction," Pezdirc said.
Most European countries have legislation allowing them to prosecute international crimes like genocide regardless of where in the world they happen. About 15 have units dedicated to investigating and prosecuting them.
Over the past decade, authorities in Europe have launched 1,607 international war crimes cases in domestic jurisdictions, while another 1,339 are ongoing, according to EU judicial cooperation agency Eurojust.
German police have compiled testimony from hundreds of potential witnesses to the Syria conflict, and war crimes prosecutors in Karlsruhe have questioned a few dozen of them in greater depth.
But gathering evidence is a painstaking process. Traumatised witnesses, fresh from harrowing journeys on foot and by sea, need time before they are ready to testify, and can often face only short periods of questioning each day.
"The refugees usually need time to rest and calm down before they decide to cooperate with law enforcement," Pezdirc said.
Investigators have interviewed Yazidi Kurd refugees in Germany for evidence of alleged genocide against the ethnic and religious minority. A German citizen thought to be in Syria is the subject of a sealed arrest warrant on separate war crimes charges.
They are preparing further cases against two other suspects, one accused of torture and another of kidnapping a U.S. legal adviser near Damascus.
In France, genocide and war crimes prosecutors have a handful of investigations open into Syrian nationals, including a former Syrian colonel, once a doctor in a military hospital, who has sought asylum.
More than 4,000 European citizens are estimated to have left to fight in Syria, of whom around a third have since returned home, a Dutch think tank said earlier this year.
With both witnesses and perpetrators on their territory, European prosecutors have already brought some cases. A German citizen is on trial for war crimes after Facebook posts showed him posing alongside decapitated heads.
Last year, Swedish courts convicted a Syrian on the basis of a video showing him torturing a fellow combatant. Crimes being investigated around the continent include torture, murder, rape, crimes against humanity and genocide.
SECURITY COUNCIL SPLIT
With more than 400,000 people killed in Syria since 2011, there have been calls for perpetrators of massacres to face trials in a U.N. court, like those that followed the Yugoslav wars of the 1990s.
But division among the five veto-wielding permanent members of the U.N. Security Council - who include Syria`s ally, Russia - has stymied attempts to refer such cases to the International Criminal Court in The Hague, or set up a special tribunal.
So rights campaigners are pinning their hopes on national prosecutions, and Syria and Iraq have come to dominate the agenda of the Genocide Network, which has been operating since 2004.
"If there`s going to be justice in Syria, it`s going to be in the courts of third states," said Stephen Rapp, a U.S. diplomat who led the prosecution of former Liberian President Charles Taylor, at a meeting of law enforcement officials in The Hague this week.
Successful trials could help to influence the wider course of the war and the migrant crisis, he said.
"If we do more to show there`s justice, that there`s hope, if we can show that this way of fighting the conflict is going to have consequences, we can reduce the refugee flow."
(Additional reporting by Chine Labbe in Paris, Stine Jacobsen in Oslo, Jussi Rosendahl in Helsinki, Rodrigo De Miguel Roncal in Madrid; Editing by Anthony Deutsch and Mark Trevelyan)