IT WAS clear that Hamza Ali al-Khateeb had been tortured before he died. Returned to his family a month after he was arrested at a peaceful protest in April 2011, the 13-year-old boy’s dead body was covered with cigarette burns and lacerations. His jaw and both kneecaps had been smashed and his penis had been cut off.

As demonstrations against the regime’s rule spread across the country, the boy’s death at the hands of the regime’s security forces became a powerful symbol of its brutality. “I can only hope that this child did not die in vain but that the Syrian government will end the brutality and begin a transition to real democracy,” said Hillary Clinton, who was America’s secretary of state at the time. During the early days of the uprising many shared her hope.

Almost six years on that hope has been crushed. The scale of the killing carried out inside Syria’s torture dungeons is difficult to gauge: human-rights groups say the regime has tortured to death or executed between 17,500 and 60,000 men, women and children since March 2011. The dead, often buried in mass graves or incinerated, are rarely returned to their relatives. The official death certificates that are sometimes handed to relatives typically say that the victims died from natural causes.

Tracking the number of people in detention is also difficult. Mr Assad’s security forces have converted sports stadiums, abandoned homes, hospitals and schools into jails. Loyalist militias from Iraq, Lebanon and Iran also operate their own secret sites. At least 200,000 people are thought to remain in detention, most of them in government facilities that are closed to the International Committee of the Red Cross.

What little is known about Mr Assad’s torture machine comes from survivors swapped in prisoner exchanges or released after bribing officials. Relatives of the dead, defectors and hundreds of thousands of government files smuggled out of the country by activists add to their accounts. Together, they paint a picture of a regime that has tortured and murdered on an industrial scale to silence dissent.

Take the case of Muhannad, a 28-year-old university student who organised some of the first peaceful protests in Aleppo. He was arrested in 2011 by agents from air-force intelligence, blindfolded and taken to a cell where he was strung from the ceiling by his wrists. He was tortured for eight days until he signed a false confession that he had killed regime soldiers with the help of his mother.

After that he was moved to an air-force intelligence base near the presidential palace in Damascus, where he underwent two years of almost daily interrogation and torture. Sometimes, for amusement, the prison guards would force the inmates to strip naked and play at being dogs. As they drank alcohol and smoked water pipes, the guards stubbed out cigarettes and tipped hot coals over the prisoners’ backs. “You have to work hard to amuse them or you get beaten,” he says.

Murder for fun

Death at the al-Mezzeh Air Force Intelligence prison was routine. Muhannad remembers how, during the month of Ramadan in 2012, the guards killed 19 prisoners in a single night. “They had brain seizures, severe bleeding from the torture,” he says.

On another occasion, a teenage boy returned to his prison cell in tears. “They’d executed his brother in front of him. Then they’d bent him over a table and raped him with a stick. They were laughing and saying ‘a new woman has been opened.’” Two other cellmates were beaten to death by guards as they waited to have their hair cut.

When the infection from an open wound in his leg spread, the guards took Muhannad to a nearby military hospital. Patients were forced to sleep with shoes in their mouths. If the shoe fell, nurses beat them with stiff plastic pipes. Muhannad says he saw a nurse club a patient to death in his bed after he asked for medicine.

It was here, at Hospital 601, that a forensic photographer working for Syria’s military police force photographed the bodies of more than 6,000 people killed in government detention facilities between 2011 and 2013. The images show rows of naked, emaciated corpses with numbers written on their foreheads. Most bear signs of torture. Smuggled out of the country on flash drives, these images provide some of the most damning evidence of the regime’s systematic use of torture.

There is little that can be done to bring Mr Assad and his thugs to justice. The UN says the regime’s use of torture and the “mass death of detainees” inside its prisons amount to crimes against humanity. Yet rights groups say that the UN, in its drive to negotiate an end to the conflict, has largely ignored the regime’s atrocities. The Security Council’s last attempt to refer Syria to the International Criminal Court failed when Russia and China objected.

“For nearly six years the Syrian people have watched Mr Assad butcher his own people. They look at him and think, ‘This person took away my son.’ How do you expect them to accept any deal that keeps the regime in power?” says Saeed Eido, who chronicles atrocities for the Syrian Institute for Justice, set up in Aleppo in 2011.

On December 2nd Syrian intelligence officials returned the dead body of Ibrahim al-Ahmed to his family. They were told that the 25-year-old, who had been missing for four years, had died of a heart attack. Yet his emaciated body, which the family barely recognised, was disfigured by missing teeth, a leg broken by a blunt tool, deep lacerations across his back, bruises and cuts. “There was no funeral. We took him straight from the fridge to the grave,” says Ibrahim’s brother. “When people in Syria know their relative has been killed in prison, they don’t make any noise about it, but it is impossible to forget.”