[4][5] The Syrian Observatory for Human Rights (SOHR) estimated in January 2021 that 30,000 detainees were killed by the Assad regime in Sednaya from torture, ill-treatment, and mass executions since the outbreak of the Syrian civil war,[6] while Amnesty International estimated in February 2017 "that between 5,000 and 13,000 people were extrajudicially executed at Sednaya between September 2011 and December 2015.

After its capture in 2024, Hayat Tahrir al-Sham published a list of escaped prison staff, who are now among the most wanted fugitives in Syria second only to members of the Assad family.

[14] The prison consists of two buildings with a total of 10,000–20,000 detainees and is under the jurisdiction of the Minister of Defense while operated by the Syrian Military Police.

[15] Locals believed that Sednaya had an underground system that extended three levels below and that it was less accessible, housing many of the most severely abused prisoners.

[16] Human rights organizations identified over 27 prisons and detention centers run by Assad's government around the country where detainees were routinely tortured and killed.

[17] A Syrian defector, known by the pseudonym Caesar, smuggled out thousands of photographs from prisons in Damascus and its periphery, providing visual evidence of detainees who had been tortured and killed.

[21][22][23] The photographs, taken over several years starting in 2013, showed building modifications that the State Department interpreted as consistent with a crematorium, though they could not definitively prove its existence.

[26][27] Of the nine killed prisoners, they were able to identify eight: Zakaria Affash, Mohammed Mahareesh, Abdulbaqi Khattab, Ahmed Shalaq, Khalid Bilal, Mo’aid Al-Ali, Mohannad Al-Omar, and Khader Alloush.

[27] Human Rights Watch, through their regional Director Sarah Leah Whitson, called on President Bashar al-Assad to immediately order an independent investigation into the police's use of lethal force at Sednaya prison.

"[26] Ammar al-Qurabi, the director of the National Organization for Human Rights, commented on SANA's release by asking to form a committee of activists which can visit the detainees and ascertain their conditions, and he confirmed that the number of prisoners in Sednaya was between 1,500 and 2,000.

After their release, many took up arms against the government and became leaders of Islamist rebel groups including Jaysh al-Islam, Ahrar ash-Sham and Suqour al-Sham Brigade in the Syrian civil war.

[33] Videos and images appeared on social media showing security cameras of imprisoned people, including families and children.

[16] Some prisoners who had been detained for decades were unaware that Bashar al-Assad's father Hafez had died in 2000 and believed he was still in power,[34] mistaking rebel troops for invading Ba'athist Iraqi forces under Saddam Hussein coming to liberate them.

[35] During the takeover, rebels discovered underground cells beneath the main prison building where dozens of men were confined in darkness.

Prisoners trapped in tunnels under the building called for help, prompting rebels to attempt breaking through concrete barriers to reach them as power outages disabled ventilation systems.

[12] Search efforts led by the White Helmets concluded on 9 December, determining that no hidden or sealed areas that could contain detainees were left.

[36] According to Fadel Abdul Ghany, director of the Syrian Network for Human Rights, approximately 2,000 prisoners emerged from Sednaya when it was liberated, though questions remained about the fate of thousands more who were believed to have been held there.

Videos obtained by The New York Times showed numbered cells that had held dozens of prisoners each, littered with debris, clothing and belongings.

[37] A wide variety of inhumane torture practices were carried out in the prison, ranging from perpetual beatings, sexual assaults, decapitations, rapes, burnings, and the use of hinged boards known as "flying carpets".

According to the report, based on interviews with former inmates, judges, and guards, groups of up to 50 people were removed from their cells for arbitrary trials, beaten, and hanged.

One former detainee, Salam, a lawyer from Aleppo, described the process: "The soldiers will practice their 'hospitality' with each new group of detainees during the 'welcome party'… You are thrown to the ground and they use different instruments for the beatings: electric cables with exposed copper wire ends – they have little hooks so they take a part of your skin – normal electric cables, plastic water pipes of different sizes and metal bars.

[46] A prisoner's testimony states: "They beat me until I was lying on the ground and then they kicked me with their military boots, in the places where I have had my hip operations, until I passed out.

[48] Amnesty International has managed to confirm the names of 375 individuals executed in Sednaya prison,[49] and while the UN Office of the High Commissioner for Human Rights and Human Rights Watch, suggests that tens of thousands of detainees have died in Sednaya and other government-run detention centers since 2011 as a result of the extermination policies,[49] Amnesty International itself calculates the number of deaths to between 5,000 and 13,000.

[47] There have repeatedly been reports on inhumane conditions for detainees in Sednaya (as well as other Syrian prisons), ranging from torture and malnutrition to spontaneous executions without fair trials.

[54] The legal and forensic teams came to the conclusion that the photos Caesar took were credible, and that they clearly showed "signs of starvation, brutal beatings, strangulation, and other forms of torture and killing.

Another former detainee is Samer al-Ahmed who, on a regular basis, was forced to squeeze his head through the small hatch near the bottom of his cell door.

She worried that their return would cause problems for her son because of his political stance, but the Syrian embassy in Saudi Arabia had assured her that this would not happen.

The internal doors were left open all the time, prisoners started to defy the security forces, and lenient treatment was obvious.

Fearing suffocation of the tear gas and the bloody scenes inside the building, the prisoners dragged some of the hostages to the roof so they could communicate with the military forces outside and find a way out of the dilemma.

The sound artist Lawrence Abu Hamdan used the technique of “echo profiling”, which made it possible for him to calculate the size of cells, stairwells, and corridors.