UN investigators say they have compiled secret lists of 4,000 perpetrators of serious crimes in Syria and hope the fall of Bashar al-Assad will help ensure accountability up to the highest level.
"It is very important that the top level perpetrators are brought to justice," said Linnea Arvidsson, who coordinates the United Nations Commission of Inquiry on Syria (COI).
"The focus should be on those who carry the main responsibility for the violations that have been committed for so many years, rather than the lower-level perpetrators," she told AFP in an interview.
Longtime president al-Assad fled Syria on Sunday as a lightning rebel offensive, spearheaded by the Islamist Hayat Tahrir al-Sham (HTS) and its allies, spectacularly ended five decades of brutal rule by the Assad clan.
Syrians across the country and around the world celebrated the end of repression in which suspected dissidents were jailed or killed, and nearly 14 years of war that killed 500,000 people and displaced millions.
The new rulers have pledged justice for victims, vowing that officials involved in torturing detainees will not be pardoned and urging countries to "hand over any of those criminals who may have fled so they can be brought to justice".
- 11,000 testimonies -
The COI has been gathering evidence of crimes committed in Syria since the early days of the civil war in 2011, and has compiled lists of alleged perpetrators.
"Up to now, we have about 4,000 names on these lists," Arvidsson said.
The lists have never been made public, but the investigators have shared details with prosecutors in jurisdictions that have investigated and brought cases against suspected Syrian war criminals.
Arvidsson said the team had "cooperated with 170 such criminal investigations", leading so far to 50 convictions for war crimes and crimes against humanity committed in Syria.
But so far, "they haven't touched the higher level perpetrators", she said.
"Now there is an opportunity opening up potentially for them also to be held accountable."
The Damascus government never granted the COI permission to enter Syria, but with Assad gone, Arvidsson said the team hoped it could gain access.
Until now, it has carried out investigations remotely, through thousands of interviews and studying mounds of documents and other evidence.
Arvidsson said the commission had more than 11,000 "testimonies" from victims of violations, detention survivors and witnesses.
- 'Profound darkness' -
The opening up of Syrian prisons has been "quite dramatic for our team for the first time to actually see and confirm... everything we have heard," the UN investigator said.
She pointed to footage from the notorious Saydnaya Prison in Damascus that showed detainees were held in "basement rooms, no windows, no light".
"That's exactly what we have been hearing for so many years from detainees," Arvidsson said.
"Some of them didn't see the sunlight for years and years... They all describe it as darkness, profound darkness."
The investigators, she said, were now "very, very concerned" about what will happen with the files found in detention facilities.
"It is incredibly important now that these (files) are protected and preserved, ideally in the site where they were found, not moved, not tampered with, not lost, not touched," she said.
The evidence was needed to secure justice. "Almost every single war crime and crime against humanity listed ... have been committed by at least one party," including "genocide", Arvidsson said.
She highlighted the "deliberate" disappearance of tens of thousands of people into Syria's feared detention network, creating "the national trauma that millions of Syrians have suffered".
"It's very important that people are held to justice for this."
The COI hopes for a national accountability process in Syria, and that steps would be taken to grant the International Criminal Court jurisdiction to prosecute crimes committed in the country.
"A combination of local and international efforts" might work, Arvidsson said. "We have a duty to leave no stone unturned in this quest".
By Nina Larson