The UN Commission of Inquiry on Syria has gathered enough evidence for President Bashar al-Assad to be convicted of war crimes, says a prominent member of the commission, Carla del Ponte.
Ms Del Ponte, 70, who prosecuted war crimes in Rwanda and former Yugoslavia, announced last week that she was stepping down from her role in frustration at the UN Security Council's failure to continue the commission's work by setting up a special tribunal for Syria that could try alleged war criminals.
She has not said when she will leave her post.
Asked in an interview with Swiss newspaper SonntagsZeitung whether there was enough evidence for Assad to be convicted of war crimes, she said: "Yes, I am convinced that is the case. That is why the situation is so frustrating. The preparatory work has been done. Despite that, there is no prosecutor and no court."
The Syrian government led by Mr Assad denies reports by the commission documenting widespread war crimes committed by government-backed forces and Syria's security services.
Ms Del Ponte, a former Swiss attorney-general, joined the three-member Syria inquiry in September 2012, chronicling incidents such as chemical weapons attacks, a genocide against Iraq's Yazidi population, siege tactics, and the bombing of aid convoys.
The commission was set up in August 2011 and has regularly reported on human rights violations, but its pleas to observe international law have largely fallen on deaf ears.
Although the United Nations is setting up a new body to prepare prosecutions, there is no sign of any court being established to try war crimes committed in the six-and-a-half year-old war. Nor is there any intention by the UN Security Council to refer the situation to the International Criminal Court in the Hague.