Tens of thousands of men, women and children have disappeared into secret detention centres in Syria since protests began in 2011. Survivors allege crimes against humanity, and they’re fighting to free those still detained and to prosecute the perpetuators at the very top of the regime.

Bill Wiley and his team of war crimes investigators are smuggling material out of Syria to a secret location in Europe. They’ve already extracted around 600,000 pages of regime documentation – a wealth of potential evidence against the Syrian regime that could help to build the case for a criminal prosecution along the lines of the Nuremberg trials. The paper trail led the prosecutors to the fate of the protestors who took to the streets in 2011. People like Mansour, Ayham and Mazen, who are mentioned in the film, were rounded up and sent to secret prisons.

Using the documents, war crimes investigators have pieced together what happened behind the scenes. Orders came from the top of the regime, identifying who should be targeted. Inside the prisons, mass executions were taking place and detainees starved and tortured. Desperate not to be forgotten, they wrote their names in blood and smuggled messages out. Outside, their relatives begged the authorities for any news.

Mazen and Mansour were eventually released. Ayham’s mother would identify him as ’corpse 320’ in a stash of smuggled photos. Haunted by what they experienced, they are now helping prosecutors. But the UN seems unable to act, as much of the international focus has been on ISIS crimes. Security council resolutions to refer Syria to the International Criminal Court have been vetoed by Russia and China.

But there is one route to justice. If one of the victims of the detention centres was European or one of the perpetrators travelled to Europe, a case could be opened in a European court. And recently, there was a major breakthrough. The sister of one of the victims is a dual Spanish/Syrian national. She has filed papers in Spain’s national court bringing a case of state terrorism.