The strength of evidence indicating that Syria's regime has undertaken "industrial-scale killing" of its opponents has been likened to that uncovered by war crimes prosecutors at the Nuremberg trials of the Nazis.
Former international prosecutors who examined photographs of about 11,000 people killed by Syrian security forces have suggested the last time such compelling evidence of atrocities on this scale was uncovered was at the end of the Second World War.
United Nations human rights spokesmen have said a report by the three eminent lawyers who assessed the Syrian government images is "extremely alarming", and the US said those responsible for such serious violations in Syria "must be held to account".
We have not seen this kind of documentation since the Nazis and Nuremberg.
Photographs recording the deaths between March 2011 and August 2013 of people being held by Syrian security forces -mostly young men - formed part of a grim exercise in stock-taking by the government of President Bashar al-Assad to confirm that its opponents had been executed.
Although the UN and human rights activists have proof of abuses by both Assad's forces and rebels, experts suggest the latest evidence - smuggled out of the country by a defector - is much more detailed and on a much larger scale.
Professor Sir Geoffrey Nice QC, one of the lawyers who examined the photographs, said he believes the evidence would support findings of crimes against humanity against the Assad government and could support findings of war crimes.
"If we are correct in judging that this evidence could be put before a tribunal, we start off with a cracking good piece of evidence unusual in its scale," Nice said.
"It's unusual and surprising - you have got to go back to Nuremberg [to encounter similarly strong evidence] where the Allies had the keys to the archives and, although it may not have been presented in public in a dramatic way like this, had an enormous amount of material that could prove the bedrock of a case that they never needed to prove by live witnesses because the written documentation was enough."
Professor David Crane, another member of the trio of lawyers who examined the photographs, also drew parallels with the past.
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"We have not seen this kind of documentation since the Nazis and Nuremberg," he said.
"We don't normally see this in modern international criminal law because we are dealing with atrocities that take place in what I call 'dirty little wars', where the parties are Third World rebels and armies who are not trained.
"This is very compelling evidence that the Assad regime has an industrial-scale killing machine grinding their own civilians into dust.
"Here in Syria, we have a systematic killing of civilians in a way that is governmentally sponsored, according to a procedure: We have bodies that show starvation and torture, they are numbered by the intelligence service, by the forensic teams, by the processing teams, they have produced reports compiling the numbers, which they then processed, signed off, stamped and forwarded up the chain in the Syrian government - and we have the individual who took the pictures.
"You really, frankly, cannot get any better evidence."
The images were smuggled out of the country on memory sticks by a former photographer with the Syrian military police - later codenamed "Caesar" - who handed them to the opposition Syrian National Movement.
The three senior lawyers who scrutinised them were Nice, of Gresham College in London, who prosecuted former Yugoslavian President Slobodan Milosevic; Crane of Syracuse University, who indicted Liberian President Charles Taylor; and Sir Desmond de Silva QC, a former chief prosecutor in Sierra Leone.
Forensic science experts also examined and authenticated the 55,000 digital images Caesar provided, which together record about 11,000 victims.
The lawyers judged Caesar "a truthful and credible witness" and their 31-page report stated there was "clear evidence, capable of being believed by a tribunal of fact in a court of law, of systematic torture and killing of detained persons by the agents of the Syrian government".
The publication of the report coincides with this week's Geneva peace conference organised by the UN that is seeking to find a solution to the Syrian crisis.
For Assad to face trial, the UN Security Council would have to refer the case to the International Criminal Court (ICC) - but this would almost certainly be blocked by Russia, Syria's close ally.
Syria's government has also sought to cast doubt on the credibility of the photographic evidence because the lawyers' report was commissioned on behalf of Qatar, which has armed opponents of Assad and called for his prosecution.
But Nice says the evidence of the crimes is so compelling it will be hard for the international community to ignore.
"This particular piece of evidence is so strong it's going to be embarrassing for the United Nations and the International Criminal Court to do nothing," he said.
"Even if the witness, or anybody else, fails to refer them to the ICC or to the UN Security Council, they are going to have to take account of it in some way or other.
"The problem really is that those organisations have shown to be wanting in this type of endeavour, and they are putting political interests ahead of justice and so may very well do absolutely nothing."
Crane said ultimately the decision to prosecute or not will be political.
"We have the ability, the jurisprudence as well as procedures and evidence, to prosecute all parties in the tragedy that has taken place in Syria, but at the end of the day it will be a political and diplomatic decision as to what the international community chooses to do related to the rule of law and to properly prosecuting all the parties that have committed war crimes and crimes against humanity."
But he added behind the politics it was important to remember what the victims had suffered.
"It doesn't matter whether they suffered more or less - every person in these situations dies horribly, in pain and alone, and so we have to show them respect."
Source: Al Jazeera