A report compiled by three international war crimes prosecutors claims that the Syrian government is behind the "systemic killing" of approximately 11,000 detainees between March 2011 and August 2013. 
The Guardian, which obtained access to the report, says that the source of the report's claims is a military police photographer who secretly worked with a Syrian rebel group before defecting and fleeing the country. In the process, the defector smuggled the images of "killed detainees" out of the country on memory sticks. 
The defector, identified in the report as Caesar, does not claim to have witnessed executions or torture himself. However, he describes the bodies of detainees, mostly young men, as being emaciated, blood-stained, and in some cases bearing signs of strangulation or electrocution. 
The report claims that "Caesar" photographed as many as 50 bodies a day. The purpose of the photographs, according to the defector, was to allow a death certificate to be produced without allowing families of the deceased to see the body, as well as to confirm that orders to execute prisoners had been carried out. Families were usually told that their loved ones died from either a heart attack or "breathing problems."
The 31-page report was commissioned by a London-based law firm operating on behalf of the government of Qatar, which has financed and armed rebel groups in Syria and repeatedly called for Syrian President Bashar al-Assad to stand trial for war crimes. Two of the report's authors Sir Desmond de Silva and David Crane, argued war crimes cases related to the 1991-2002 civil war in Sierra Leone, while the third author, Sir Geoffrey Nice, led the prosecution of former Serbian leader Slobodan Milosevic at The Hague. 
The publication of the report is believed to be timed to coincide with this week's peace conference in Geneva, which has been convened with the hope of creating a transitional government. 
British Foreign Secretary William Hague called the report "further evidence of the systematic violence and brutality being visited upon the people of Syria by the Assad regime. We will continue to press for action on all human rights violations in Syria, and for accountability for those who perpetrate them."