Every day, the bodies were delivered to the hospital: battered beyond belief and hideously scarred from months of the most horrific torture imaginable.

The corpses were shrivelled from dehydration and starvation, with ribs sticking out and limbs like sticks.

Most were covered in purple bruises from beatings, and many were criss-crossed with wounds from knives, or burns from acid, electricity or cigarettes.

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Distressing photographs of corpses shrivelled from dehydration and starvation, with ribs sticking out and limbs like sticks have been obtained by the Mail on Sunday

One was missing an eye, gouged out during frenzied beating. Another had no head. A third showed signs of acid dripped along the victim’s back, the vertebrae visible through terrible holes in flesh. Others were riddled with disease.

These were the victims of Syria’s slaughterhouses: the jails and prisons run by President Bashar Assad’s regime, designed to terrorise the Syrian people into submission after they dared rise up in revolt.

And inside three Damascus hospitals, doctors were forced to cover up the depravity by signing certificates saying the victims died from conditions such as heart failure or breathing difficulties.

‘It was like a scene from hell

‘It was like a scene from hell. We did not even have time to check if they were dead,’ said one of the doctors known as Nemer Hassan. ‘I have seen so many terrible things.’

Then the corpses were whisked away to nearby mass graves, buried in their thousands without families being informed, in an effort to hide evidence from any war crime investigations. Such is the appalling banality of evil: industrial-scale torture and murder, backed by a cold bureaucracy to cover up the most revolting crimes of this century.

Little wonder that UN experts asked to review the photographic evidence compared such scenes with the horror of Nazi death camps.

Sir Desmond de Silva, who co-authored a UN report into Assad’s atrocities, said the photographs are ‘reminiscent of pictures of people who came out of Belsen and Auschwitz’.

These are the victims of Syria’s slaughterhouses: the jails and prisons run by President Bashar Assad’s regime, designed to terrorise the Syrian people into submission after they dared rise up in revolt

His view was echoed by forensic anthropologist Professor Sue Black, who said reviewing the evidence for the UN had been like ‘going back in time and looking at concentration camps’.

She added: ‘In this day and age, you really don’t expect to be able to witness these sort of things on this sort of scale.’

In a barbaric twist, it was hospitals – designed as sanctuaries for the sick – that were used to serve the sadistic inhumanity of a blood-stained dictator, who trained in Britain as an eye doctor.

It was here that Nemer – not his real name, to protect his family – was forced to serve. Speaking to The Mail on Sunday last week in the German city where he now lives, this affable man in his 30s told tales of depravity and despair.

His evidence formed part of a damning report last week by Amnesty International, which claimed up to 13,000 people have died in a ‘calculated campaign of extrajudicial execution by mass hangings’ at one notorious jail alone.

It was dismissed by Assad as ‘fake news’ – just as he dismissed thousands of images of emaciated dead torture victims smuggled out by a security forces photographer. These led last week to the launching of a landmark human rights case in Spain against senior Syrian figures.

But revelations from those such as Nemer – so chilling and resonant from the worst chapters of recent European history – expose what has gone on behind the closed doors of Assad’s torture chambers.

When the uprising against Assad began in 2011, Nemer was training as a surgeon in Tishreen, a huge hospital in Damascus built by the French and run by Syria’s Military Medical Services.

As protests swelled, Syria’s four rival intelligence bodies began dumping dozens of torture victims at the hospital for treatment

‘The dream of every Syrian is to be a doctor since it is a respected, secure and well-paid job,’ he said. ‘And I liked the idea of helping people.’

But he soon found himself in a moral quagmire. One day in April two buses, a truck and an ambulance pulled up. They were stuffed with Syrians who had been shot taking part in unarmed protests.

‘It was horrible to see them arrive. They had bullet wounds in their legs and backs but the military police were kicking them on the injured areas as they left the buses.’

He witnessed one security goon switch off a ventilator keeping an old man alive in the ambulance. ‘We were so surprised to see this – they would not even give him a chance.’

The remainder were taken to an underground emergency room, handcuffed to each other and laid across 200 beds in four rows.

Some beds held more than one injured protester. ‘I saw the military police walk across the patients, jumping on them. It was designed to hurt as much as possible,’ said Nemer.

The young doctor began to sterilise his hands to treat a man whose thigh had been shattered by a bullet. ‘Why do that for these animals?’ asked one military colleague, a member of the Alawite sect like Assad. ‘These people are polluted.’

Days later, a video from inside the emergency room was leaked on to social media. Security forces immediately placed armed guards on the doors and banned non-Alawites – especially Sunni Muslims such as Nemer – from entering.

But within weeks, as protests swelled on the streets, Syria’s four rival intelligence bodies began dumping dozens of their torture victims at the hospital for treatment.

I asked Nemer why he thought they spared some people? ‘They wanted to deliver a message to the wider community: this is what will happen if you fight us,’ he replied.

Assad’s foes were not safe, however, even in hospital. Medics would return to patients they had treated hours earlier to find new burns on their bodies – or fouled water from toilets poured on bandages covering freshly cleaned wounds.

‘There were days we felt so desperate. It was just disgusting,’ said Nemer.

A damning report by Amnesty International claimed up to 13,000 people died in a ‘calculated campaign of extrajudicial execution by mass hangings’ at one notorious jail alone was dismissed as 'fake news' by President Assad (pictured)

‘I would carry out an operation under anaesthetic, clean up wounds, use antibiotics and then screw an external metal fixation on to the bones to hold an arm or leg together. But when I went back, someone from intelligence had pulled it out. Can you imagine the pain that must have caused?’

The doctors complained about the killings and torture, saying they were in a hospital ‘not a slaughterhouse’, but security chiefs brushed aside concerns. Nemer would try to find out names of those chained to the beds, passing on the details to their families.

This is a hospital not a slaughterhouse

Security officials sometimes casually stubbed out cigarettes on patients when he walked into a room. Yet incredibly, below these atrocities on the eighth-floor, was a regular hospital, which was even used as a showcase for visiting dignitaries. Eventually, Nemer found it too traumatic – especially since he was moonlighting in secret field hospitals to help injured protesters.

When a mortar exploded in one attack, he rushed outside and almost trod on the severed head of a doctor friend who had taken a break.

He was also routinely interrogated for days on end by intelligence officials, who did not trust him since he was Sunni and his roommate was under suspicion.

‘I asked to move to another hospital because I could not handle the situation any longer.’ His request was granted.

Yet Nemer’s life did not improve when he went to Harasta hospital, on the outskirts of Damascus – for the intelligence agencies began documenting their dead and he was forced to collaborate with their activities.

‘Every day they would bring corpses in a jeep or truck. The officials would tell us to write death certificates and we had to ignore the obvious signs of torture and starvation. They would not even let us take a pulse or examine the pupils.’

UN experts asked to review the photographic evidence compared such scenes with the horror of Nazi death camps.

One day after a big battle in Damascus, there were 1,300 bodies. More typically, a flatbed truck would arrive with 20 or 30 destroyed corpses on the back; once, he saw a body slip on to the pavement after a driver took a hospital roundabout too fast.

‘The first time I refused to sign the death certificate but an intelligence person held his AK-47 to my head and said, “Do it or die.”

‘It was such humiliation – inside you’re boiling with anger but you can’t do anything. This hurt so much. I am a doctor. When I graduated I took the Hippocratic Oath, which was about saving lives.’

Pictures of the battered, burned and starved bodies were captured by a military police photographer

known as Caesar, who smuggled out more than 53,000 images on memory sticks to provide evidence of Assad’s brutality.

The corpses had codes scribbled on skin: the identity number; the unit that killed them; the hospital case file number. It was just like the Nazis documented their evil deeds – and, indeed, just as Islamic State catalogue Yazidi women sold into sex slavery.

BORIS: I'M SICKENED. NOW END THIS BARBARIC REGIME by Glen Owen for the Mail On Sunday Foreign Secretary Boris Johnson has expressed his horror over the pictures Foreign Secretary Boris Johnson has expressed his horror over the pictures obtained by The Mail on Sunday – and said that they had redoubled his determination to work for the removal of the Assad regime. Mr Johnson said last night: ‘The sickening images show the utter barbarism of Assad and his regime. He has blood on his hands and is responsible for the majority of the 400,000 people killed in Syria over the past five years. ‘He cannot command the loyalty of the people on whom he has inflicted so much suffering and there must be a transition away from this barbaric regime.’ The recent evidence of human rights abuses in Syria has hardened the Foreign Secretary’s resolve after he had appeared to soften his stance last month, when he floated the idea of Assad being permitted to run for election as part of a ‘democratic resolution’ of the civil war. Mr Johnson made the remarks after new US President Donald Trump had thrown the Anglo-Washington position into doubt by using one of his first interviews after winning the election to say that his focus would be on defeating Islamic State in Syria rather then toppling Assad. ‘I’ve had an opposite view of many people regarding Syria. My attitude was you’re fighting Syria, Syria is fighting IS, and you have to get rid of IS,’ Mr Trump had said. But at a Cabinet meeting on Tuesday, Mr Johnson declared that after the torture revelations, he no longer thought that Assad was fit to ‘take control of its democratically elected government’. Advertisement

‘This was when Assad started telling the international community that he was fighting terrorists. He began documenting everything so he could say, if challenged, that all these prisoners died from natural causes.’

Nemer smiled ruefully before adding: ‘And if the certificates were signed by a Sunni doctor, that gave them more protection to argue it was legitimate.’

The UN agreed in December to start gathering evidence as a step towards prosecuting those behind Syria’s atrocities.

But since Russia joined Iran in propping up Assad, it seems increasingly likely he will cling on to power – no wonder he could say last week he ‘doesn’t care’ about war crimes.

‘Every day they would bring corpses in a jeep or truck

Nemer stayed because, like other doctors, he was secretly undermining Assad by signing sick notes for scores of military recruits, knowing they would flee if allowed to return home.

Some were so desperate to escape they even shot themselves. Then the surgeon was warned by a friend that he was about to be arrested for anti-regime activities.

Nemer fled instantly, bribing his way into rebel-held areas before crossing the border to Turkey. Sadly, his elderly father ignored warnings not to return after getting cancer several months later – and with dreadful irony, died in Harasta hospital after being seized by security forces and beaten savagely in a detention centre.

One more dead person in a war that destroyed a nation.

But at least brave people such as Nemer are bearing witness to evil, speaking out to remind us of the war crimes being committed on all sides of this century’s most distressing conflict.