Footage has emerged of what appears to be opposition fighters killing an unarmed man in the Syrian village of Harem.
Rebels went house-to-house targeting people they say were loyal to President Bashar al-Assad and his army.
The United Nations has said both government forces and rebels are guilty of war crimes, including prisoner executions, and the latest video appears to be yet more evidence.
It could not have come at a worse time for Syria's diverse rebel factions, who are trying to persuade the world's governments they are worth supporting.
Al Jazeera's Michael Morrah reports.