(CBSNews.com) - A day before Wednesday's Syria peace conference in Switzerland, a new report by former war crimes prosecutors contains photographic evidence that seems to show a mass killing by the regime of Syrian President Bashar Assad.
According to the report, some of the victims were beaten, some were strangled, and others were starved.
One of the report's authors described it as killing on an industrial scale.
The pictures come from a defector who worked for Syria's military police as a photographer. He told investigators his job was to photograph the bodies of dead prisoners after they were taken to a military hospital.
Thousands of his images were examined by an international legal and forensic team who found his account believable, and concluded there is "clear evidence... of systematic torture and killing of detained persons by the agents of the Syrian Government."
They estimate the photographs document the torture and execution of 11,000 people over a two and a half year period during the Syrian conflict.
CBS News cannot independently verify the images. The report was funded by the Qatari Government, which supports the Syrian opposition.
But the authors are experienced former war crimes prosecutors, including Sir Desmond De Silva.
"This has all the hallmarks of ordered... deliberate.. merciless execution, by a whole variety of unpleasant means," De Silva said.
Both the Syrian army and the rebels have been accused of atrocities during thecountry's civil war, which they have been fighting now for nearly three years.
But the scale of the torture and executions alleged in this report is unprecedented.
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