A court in Germany has charged two suspected former Syrian intelligence officers with crimes against humanity.
One of them, Anwar R., is suspected of being involved in the torture of at least 4,000 people in 2011-12. This resulted in the deaths of 58 people.
The other suspect, Eyad A, is charged with torture in at least 30 cases.
Key evidence was gathered after a UN exhibition in 2015, which depicted the corpses of torture victims in Syria under President Bashar al-Assad.
The trial of the two men, who were arrested in Berlin and Rhineland-Palatinate state in February, is expected to start in the western city of Koblenz early next year.
Neither the suspects nor President Bashar's government have commented on the case.
What are the men accused of?
German federal prosecutors say the two men had been members of Syria's General Intelligence Directorate (GID) in the Damascus area.
They allege that Anwar R., who is 56, was a high-ranking officer who led the branch's investigative department, and that he assigned and directed operations at a prison where detainees were subjected to "systematic and brutal torture".
Eyad A., 42, is alleged to have worked for Anwar R.'s department.
1/2 German prosecutor charges former Assad regime officials over alleged mass torture. Syrian survivors and lawyers in Germany have been fighting for this for months.... https://t.co/UxpoFYJmFn— jenny hill (@jennyhillBBC) October 29, 2019
"These charges send an important message to survivors of Assad's system of torture," said Wolfgang Kaleck, Secretary General of the European Center for Constitutional and Human Rights (ECCHR).
"We will continue working to ensure that the main perpetrators of state torture under Assad are brought to justice - in Germany or elsewhere," he added.
Key evidence against the two suspects was obtained after the exhibition at the UN headquarters in New York in March 2015.
The pictures were taken by "Caesar", a former member of the Syrian military police who fled the country in 2013.
Anwar R. and Eyad A. seem to have sought asylum in Germany after leaving Syria a few years before the migrant influx in 2015.
The GID is Syria's most powerful civilian intelligence agency and it has been accused of playing a key role in the violent suppression of the peaceful protests against Mr Assad's rule that erupted in March 2011.
Are there other cases?
German officials say they are investigating dozens of other former Syrian officials under the principle of "universal jurisdiction", which allows courts to try individuals suspected of committing genocide, crimes against humanity, and war crimes.
Last year, German prosecutors issued an international arrest warrant for Jamil Hassan, the head of Syria's Air Force Intelligence service, accusing him of overseeing the torture, rape and murder of hundreds of people between 2011 and 2013.
Syria's government has denied taking political prisoners. It has also denied torturing or killing anyone in custody.
Some of those survivors told us their story earlier this year pic.twitter.com/1XFGdolPwG— jenny hill (@jennyhillBBC) October 29, 2019
However, UN human rights experts said in a report last March that government forces and affiliated militias were "arbitrarily or unlawfully detaining tens of thousands of individuals in official and makeshift detention centres".
"They endure various forms of brutal torture and subsist in severely inhumane conditions. Many have died in detention, while others have been summarily executed," they added.
The bodies of those detainees who have died are rarely returned to their families, who are also not notified about burials, according to the UN experts. As a result, their whereabouts remain unknown.
The Syrian Network for Human Rights (SNHR), a campaign group, said in August that it had documented the deaths of more than 13,600 people due to torture in prisons operated by parties to the war in Syria, with more than 90% occurring in government-run facilities.