Harrowing final words of tortured prisoner executed in 'human slaughter house'

The conditions inside Bashar Al-Assad's 'human slaughterhouse' prisons in Syria were beyond most people's worst nightmares. Thousands of people died inside them, or vanished - but everyone incarcerated within them suffered.

Torture was a daily horror, not just in the much-dreaded interrogations, but in the conditions within which the prisoners were held in such close proximity that some are even said to have suffered psychosis from oxygen deprivation.

When his oppressive regime was finally overthrown, relatives of those who had been imprisoned flooded into the facilities, desperate for answers about where their loved ones had gone, and footage was recorded of families searching frantically through debris for any clue of their fates.

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Prisoners were fed like animals from large pails, and lived in such cramped conditions that guards revealed it was not possible to see the floor. At the Air Force Intelligence branch in Harasta, conditions could not have been more hellish.

The once-second-in-command of the facility, Colonel Zain, hauntingly admitted: "The place I worked in was very famous for its bloody practices and the number of detainees held there. We would pack 400 detainees in a room that was eight by ten metres.

"You wouldn't set eyes on the floor when you entered; bodies of detainees blanketed it. The screams emanating from the interrogation room situated directly below my office were no secret. It was common knowledge how we conducted our interrogations.

"The temperature was around 40 degrees, because it was so crowded. We saw strange cases of disease amongst prisoners, I think, due to oxygen deficiency because of overcrowding. These psychotic episodes soon turned into physical symptoms," he said to BBC Two's documentary Surviving Syria's Prisons.

It has been estimated by Amnesty International that 13000 people died in these nightmare slaughterhouse prisons in just the first four years after the Arab Spring in 2011, which, after a brief hope it might bring better times, swiftly turned into a hellish civil conflict, with protests in Damascus put down ruthlessly.

Inside these prisons, guards tortured - often entirely false - confessions from prisoners, threw execution parties, and were even told to "bury them alive".

Hussam, another guard and former military policeman, told the BBC of the haunting last words of a prisoner who faced execution, and the extensive torture they inflicted on prisoners.

"Our superiors would say, 'Torture them, don't let them sleep at night. Throw them a party... put them in a grave if you want to, bury them alive'.

"When they'd call me to go and torture them, the prisoners would go back to their cells bloody and exhausted. On Wednesday mornings, we'd have an 'execution party'. Our role during executions was to place the rope on the prisoner - only an officer could push the chair."

He continued, "One time, the chair was pushed, but after 22 minutes he didn't die. So I grabbed him and pulled him downwards, so another guard who was bigger and stronger said, 'go I will do it.' Before he died he said one thing: 'I'm going to tell God what you did'."

An army nurse revealed in the documentary that they were not allowed to record the real causes of death, whether that was extensive torture or execution. "It was forbidden to record the cause of death as torture. Even those killed from gunshots were recorded as heart and respiratory failure."

Over 130 mass grave sites have so far been discovered in Syria, with families facing the distressing prospect of struggling to identfiy their loved ones amongst the countless dead.