Zahira (not her real name) was 45 when she was arrested at her workplace in a suburb of Damascus in 2013. As soon as she arrived at Al Mezzeh Military Airport, she was strip searched, tied to a bed and gang raped by five soldiers.

For the next 14 days, she was raped, or threatened with rape, again and again and again.

During one interrogation, in which she says she was sexually penetrated in “every body cavity”, a soldier filmed what was happening and threatened to show it to her family and community.

Shunted from facility to facility over the course of five months, in addition to repeated brutal sexual violence Zahira was also regularly beaten. One one occasion she was electrocuted and beaten with a hose pipe; on another, tied upside down for over an hour and hit in the face.

Between interrogations at Al Mezzeh she was held in solitary confinement, in a cell no bigger than one metre by one metre, with no natural light.

In Military Intelligence Branch 235, she slept in a three by four metre cell with up to 48 other women that was so cramped the prisoners had to sleep in shifts. They were allowed to use the toilet once every 12 hours, and to wash once in every 40 days.

Zahira was only released from the notorious Adra prison when the conditions affected her health so severely she lost consciousness and was taken to hospital, her jailers fearing they’d killed her.

On arrival at a medical facility doctors found she had hepatitis, pneumonia and anaemia. She had to stay in hospital for four months for corrective surgeries for faecal-urinary incontinence caused by her repeated rapes.

The woman’s story is not easy to read. Experiencing what she went through is beyond the imagination of most of us.

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But Zahira, and dozens of other brave women, have shared their stories with a network of exiled Syrian doctors and lawyers, who have documented what happened to them in Syrian President Bashar al-Assad’s prisons in a new report.

One pregnant woman, arrested because the government suspected her husband of supplying medicine to rebel forces, describes seeing dead bodies dragged through corridors, leaving them slick with blood. The screams of those being tortured still haunt her.

Another former detainee described being locked in a pitch black cell for six days with a dead body. A razor blade had also been purposefully left there, and she used it to try and kill herself.

The physical and mental scars from detention will affect these women for the rest of their lives. Many feel shame, and their relationships with their families and communities has changed because of the stigma attached to sexual assault and rape.

Their hope is that shedding a light on what happens in Assad’s detention centres will amount to international pressure to allow inspectors into the country and thus stop the government acting with impunity.

What their testimony also means, however, is that officials in Syria’s government, police and military could be held accountable for their actions in potential future war crimes trials.

In Pictures: The crisis unfolding in Syria Show all 30 1 /30 In Pictures: The crisis unfolding in Syria In Pictures: The crisis unfolding in Syria A Syrian family arrives at a checkpoint, manned by pro-government forces, at the al-Hawoz street roundabout, after leaving Aleppo's eastern neighbourhoods Getty In Pictures: The crisis unfolding in Syria A Syrian woman, fleeing violence in the restive Bustan al-Qasr neighbourhood, reacts as she stands with her children in Aleppo's Fardos neighbourhood, after regime troops retook the area from rebel fighters Getty In Pictures: The crisis unfolding in Syria Syrian pro-regime fighters, gesture as they drive past resident fleeing violence in the restive Bustan al-Qasr neighbourhood, in Aleppo's Fardos neighbourhood Getty In Pictures: The crisis unfolding in Syria Syrian rebels withdrew from six more neighbourhoods in their one-time bastion of east Aleppo in the face of advancing government troops, the Syrian Observatory for Human Rights said Getty In Pictures: The crisis unfolding in Syria Syrian rebels withdrew from six more neighbourhoods in their one-time bastion of east Aleppo in the face of advancing government troops, the Syrian Observatory for Human Rights said Getty In Pictures: The crisis unfolding in Syria Syrian residents, fleeing violence in the restive Bustan al-Qasr neighbourhood, arrive in Aleppo's Fardos neighbourhood , after regime troops retook the area from rebel fighters Getty In Pictures: The crisis unfolding in Syria Syrian pro-regime fighters, gesture as they drive past residents fleeing violence in the restive Bustan al-Qasr neighbourhood, in Aleppo's Fardos neighbourhood Getty In Pictures: The crisis unfolding in Syria Syrian residents, fleeing violence in the restive Bustan al-Qasr neighbourhood, arrive in Aleppo's Fardos neighbourhood, after regime troops retook the area from rebel fighters Getty In Pictures: The crisis unfolding in Syria Syrian residents, fleeing violence in the restive Bustan al-Qasr neighbourhood, arrive in Aleppo's Fardos neighbourhood Getty In Pictures: The crisis unfolding in Syria A Syrian pro-regime fighter speaks with a child, as residents flee violence in the restive Bustan al-Qasr neighbourhood. Syrian rebels withdrew from six more neighbourhoods in their one-time bastion of east Aleppo in the face of advancing government troops AFP/Getty Images In Pictures: The crisis unfolding in Syria Smoke rises as seen from a governement-held area of Aleppo, Syria Reuters In Pictures: The crisis unfolding in Syria Syrian soldiers targeting rebels-held areas in the eastern neighborhoods in Aleppo, Syria. According to media reports, the army is now holding on 99 percent of Aleppoís eastern neighborhoods EPA In Pictures: The crisis unfolding in Syria Syrian pro-government forces patrol Aleppo's eastern al-Salihin neighbourhood after troops retook the area from rebel fighters Getty In Pictures: The crisis unfolding in Syria Syrian soldiers rest following the battle at al-Sheik Saeed neighborhood in Aleppo, Syria EPA In Pictures: The crisis unfolding in Syria A Syrian pro-government fighter walking past closed shops in the Bab al-Nasr district of Aleppo's Old City. Once renowned for its bustling souks, grand citadel and historic gates, Aleppo's Old City has been rendered virtually unrecognisable by some of the worst violence of Syria's war Getty In Pictures: The crisis unfolding in Syria The crucial battle for Aleppo entered its 'final phase' after Syrian rebels retreated into a small pocket of their former bastion in the face of new army advances. The retreat leaves opposition fighters confined to just a handful of neighbourhoods in southeast Aleppo, the largest of them Sukkari and Mashhad Getty In Pictures: The crisis unfolding in Syria Syrian civilans arrive at a checkpoint, manned by pro-government forces, at the al-Hawoz street roundabout, after leaving Aleppo's eastern neighbourhoods. Syria's government has retaken at least 85 percent of east Aleppo, which fell to rebels in 2012, since beginning its operation Getty In Pictures: The crisis unfolding in Syria Syrian civilians flee the Sukkari neighbourhood towards safer rebel-held areas in southeastern Aleppo Getty In Pictures: The crisis unfolding in Syria Syrians celebrate in the government-held Mogambo neighbourhood of the northern Syrian city of Aleppo, after rebel fighters retreated into a small pocket of their former bastion in the face of new army advances Getty In Pictures: The crisis unfolding in Syria Syrians celebrate in the government-held Mogambo neighbourhood of the northern Syrian city of Aleppo, after rebel fighters retreated into a small pocket of their former bastion in the face of new army advances. The fall of Aleppo would be the worst rebel defeat since Syria's conflict began in 2011, and leave the government in control of the country's five major cities Getty In Pictures: The crisis unfolding in Syria A Syrian refugee camp in the Bekaa Valley, Lebanon, close to the Syrian border PA wire In Pictures: The crisis unfolding in Syria Syrian refugee Aliya inside the tent where she lives with her husband and ten children in a camp in the Bekaa Valley, Lebanon, close to the Syrian border PA wire In Pictures: The crisis unfolding in Syria Syrian refugee women and children outside the entrance to their tents in the refugee camp in the Bekaa Valley, Lebanon, close to the Syrian border PA Wire In Pictures: The crisis unfolding in Syria A Syrian refugee camp in the Bekaa Valley, Lebanon, close to the Syrian border PA wire In Pictures: The crisis unfolding in Syria A Syrian refugee camp in the Bekaa Valley, Lebanon, close to the Syrian border PA Wire In Pictures: The crisis unfolding in Syria A Syrian refugee woman outside the entrance to the tent where her family live, in the refugee camp in the Bekaa Valley, Lebanon, close to the Syrian border PA wire In Pictures: The crisis unfolding in Syria A vehicle drives past a mosque at night in Idlib, Syria. Picture taken with a long exposure Reuters In Pictures: The crisis unfolding in Syria Damaged buildings stand in the rebel-controlled town of Binnish in Idlib province, Syria Reuters In Pictures: The crisis unfolding in Syria The night sky is seen through damaged windows in the rebel-controlled town of Binnish in Idlib province, Syria Reuters In Pictures: The crisis unfolding in Syria Damaged buildings stand in the rebel-controlled area of Maaret al-Numan in Idlib province, Syria Reuters

“This might be the most powerful evidence we have, the international lawyers say,” one neurosurgeon and founding member of Syrian NGO Lawyers and Doctors for Human Rights (LDHR) said on the phone from Gaziantep, on the Turkish-Syrian border.

“This is one of our best chances to get justice for these crimes against humanity.”

There has been precious little in the way of legal redress for any of the victims of Syria’s complex six-year-old war so far. There are few avenues open to them.

Carla del Ponte, a distinguished international war crimes prosecutor, resigned from her position on the UN’s investigative panel into human rights abuses in the civil war earlier this month because she was so frustrated with its inability to hold criminals to account.

“I give up. The states in the [UN] Security Council don’t want justice,” she told media when it emerged she had quit.

The Security Council, she said, should have appointed a court similar to those for the Rwanda and Yugoslavian conflicts – a decision vetoed by permanent member Russia, which is a key backer of the Assad government.

While the investigative panel has compiled thousands of interviews and other documentation of possible war crimes committed by all sides in Syria, the work was pointless without a tribunal, she added.

“We have had absolutely no success” holding perpetrators of war crimes in Syria to account, the prosecutor said. “For five years we’ve been running up against walls.”

Faced with a powerless UN and no prospect of an International Criminal Court tribunal, transitional justice and human rights lawyers have begun trying new tactics.

In March, a Spanish court agreed to hear the case of the torture and death of a 43-year-old truck driver at the hands of the Syrian government, because the man’s sister, a Spanish citizen, was the plaintiff.

Under international law relatives of victims of crimes against humanity committed elsewhere are also counted as victims – so the Spanish judge’s decision to hear it was viewed as an important landmark for potentially prosecuting high-level Syrian officials.

Guernica 37 International Justice Chambers, the Madrid-based legal advocacy group that bought the case, said in a statement it would “specifically allow the courts to investigate the torture and execution of thousands of civilians in the illegal detention centres” operated by the Assad government.

It could also mean international arrest warrants could be issued for the nine Syrian officials named in the complaint – meaning their assets could be seized or they could be charged if they travel abroad.

While the decision was reversed due to a split panel of Spanish judges last month, the case has been appealed. Stephen J Rapp, a former United States ambassador at large for the Office of Global Criminal Justice and current nonresident fellow at The Hague Institute for Global Justice, who helped to file the preceedings, told The Independent if necessary they would fight it to the Spanish Supreme Court.

“The attorneys of Guernica 37 are quite confident regarding the law and of eventual success,” he said.

“Given the years of pain that has been visited on tens of thousands family members of persons who have been forcibly disappeared into Syrian government custody this is also a very important issue of principle.”

Buoyed by the progress in Spain, Syrian victims and survivors now living in Germany have also filed a prosecution case based on an investigation by the NGO the European Centre for Constitutional and Human Rights (ECCHR).

This represents another type of case – one based on the concept of universal jurisdiction, which allows states to claim criminal jurisdiction over an accused person regardless of where their crimes were committed because of the severity of the allegations.

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More than 65,000 people are thought to have died in the Syrian regime’s prisons over the last six years, and thousands and thousands more have faced abhorrent treatment in detention. The allegations are crimes against humanity - and are thus too serious to tolerate jurisdictional arbitrage, the prosecutor will argue.

LDHR’s activists are hopeful that their findings – compiled under the Istanbul Protocol, the UN’s methodology on how to recognise and document signs and symptoms of torture so the documentation may serve as valid evidence in court – will be presented as evidence in future cases constructed on the same basis.

“There were too many women to choose from, with horrible stories, when we set about compiling this report," the LDHR doctor said.