BBC Arabic's investigations unit has pieced together the story of a so-called "double tap" airstrike on a market in Syria's Idlib province in which 39 people were killed. Nader Ibrahim explains how they put the story together, when it's too dangerous to go there, and Russian air force authorities deny it ever happened.

Picture: Emergency workers in rubble of bombed Maarat al-Nurman market, Idlib Province
Credit: Hadi al-Abdallah/YouTube