Beirut - In early May, hundreds of detainees at Syria's Hama central prison went into a week-long revolt to protest against the planned transfer of five inmates to the notorious Sednaya prison near Damascus, purportedly so that they could be executed.
The prisoners, many of whom are held without charge, rioted in solidarity.
Seven prison guards were taken hostage. Prisoners demanded "basic rights," including a fair trial or release.
A deal, however, was soon reached resulting in the release of 83 prisoners held without charge.
Two weeks later, a similar scene played out again when inmates captured a high-ranking police officer to protest at what they say was the government's reneging on an earlier deal to release several hundred political detainees.
Inmates have previously demanded the restoration of electricity and water amid food shortages and serious medical conditions among prisoners, according to to UK-based Syrian Observatory for Human Rights.
Both incidents highlighted the plight of thousands of detainees who are languishing in government prisons in appalling conditions. Both rights groups and opposition negotiators had hoped the first Hama standoff would push Syria's forgotten detainees back to the forefront of the Syria peace talks.
"As the whole world has come to know, the brave prison revolt that detainees in Hama prison staged has restored the issue of detainees to the forefront of media and international attention," wrote Anas al-Abdah, president of the opposition's National Coalition, to the International Syria Support Group (ISSG) in mid-May.
As the popular uprising, that broke out in March 2011, has turned into an armed conflict, rights groups say that both government and anti-government forces have arrested thousands of activists and civilians.
Those detainees have no voices. Nobody knows anything about them.
Between 2011 and 2015, the Syrian Network for Human Rights documented the arrest and detention of more than 117,000 people mostly by government security forces. The Syrian observatory, however, put the number at 500,000 detained and disappeared during the same period.
Last April, the main opposition negotiating group, High Negotiations Committee (HNC), said it has a list of 150,000 detainees. An unknown number of detainees are held by rebel armed groups.
According to a recent observatory report, more than 60,000 people have been killed through torture or have died in dire humanitarian conditions inside regime prisons during the country's five-year uprising - although other monitoring groups, such as the Syrian Network for Human Rights, quote lower figures.
Different numbers come down to different methodologies.
In a December 2015 report, Human Rights Watch said that its researchers had found "evidence of widespread torture, starvation, beatings, and disease" in government jails and detention centres. UN investigators and human rights groups have documented abuses inside these facilities amounting to war crimes.
Frustrated by a lack of progress from the official opposition and the international community, Syrian activists in Europe launched a new campaign last month ito refocus attention on the plight of tens of thousands of people detained or disappeared in the past five years.
The Detainees First Campaign held its first protest in central Paris on June 11. According to the campaign's founding statement: "There is international responsibility towards the continuance of the incarceration of detainees and kidnapped everywhere in Syria, whether at the hands of the Syrian regime … or at the hands of various warlords."
According to Syrian journalist and activist Sakher Idris, a member of the Detainees First, the campaign aims to to spotlight those held - especially those in secret prisons - whether in Syrian regime areas, or other opposition-held areas. "Those detainees have no voices," he added. "Nobody knows anything about them."
The campaign includes activists, artists, actors and journalists from Syria. Some have had their own experience with imprisonment, including Idris himself.
Idris's father and uncle were arrested in the mid-1970s, faced political charges under Syria's Emergency Law and were thrown into prison. They would not be released until 1991, under the first in a series of prisoner amnesties implemented by Hafez al-Assad, father of the current president.
Idris says harassment from the authorities was enough for them to leave the country.
For Idris, past informs the present. "This is a habit of the regime," he said. "They've been detaining people for a long time. And they've been detaining people since the first days of the  revolution."
In November, a UN Human Rights Council report , based on 621 interviews, accused the Syrian government of war crimes and crimes against humanity, including "extermination" in its detention facilities. It claimed that "tens of thousands of people are detained by the Syrian Government at any one time".
The report found that other parties to the conflict, including armed opposition groups such as the al-Nusra Front and the Islamic State of Iraq and the Levant group (ISIL, also known as ISIS), were also guilty of war crimes - including torture and summary executions. "The situation of detainees is critical, and represents an urgent and large-scale crisis of human rights protection," it added.
Staffan de Mistura, the UN's special envoy to Syria, recently appointed Eva Svoboda, formerly of the International Committee of the Red Cross, to handle the issue of those being held and disappeared persons as part of the ISSG's humanitarian task force - seemingly in an attempt to reinvigorate trust- on both sides.
International diplomats have long said that discussions about detainees, as well as mutual prisoner releases, could provide a key confidence-building measure going in to future talks.
Yet the very future of the Syria peace talks remains uncertain.
On Tuesday, De Mistura said that the UN would not hold another round of Syria peace talks until officials on all sides agreed the parameters for a political transitional deal.
Additionally, Mohammed Alloush, Jaish al-Islam representative and chief negotiator with the opposition's HNC, the opposition platform created in Saudi Arabia last December, recently resigned from his position.
Alice Mufarej, a member of the HNC's human rights team, said that the onus for the success of future negotiations on Syria's detainees depends on the international community and the Syrian regime. "The [HNC] negotiating team has not failed to complete the detainees file, the international community has failed to implement its legal and ethical obligations … and force the regime to respect UN resolutions."
"The regime is trying to politicise the detainees file, to use it as pressure and blackmail during negotiations," Mufarej claimed, adding that the HNC has made repeated demands for the regime to halt executions, release political prisoners - particularly women and children - and allow international inspections of detention sites.
However, Mufarej added, there had been little progress until now. Government negotiators have previously disputed the opposition's numbers on those held in Syria.
Idris, from the Detainees First campaign, says that activists, frustrated by the politics of the negotiating table, must now take matters into their own hands. "We have to try and put pressure on the negotiations, to pressure governments," he said.
"The international community has ignored this case. The media has been absent. They're always talking about air strikes, or about Daesh [ISIL], while forgetting what the regime does," Idris argued. "OK - but where are the detainees?"