I wouldn't be surprised if the informtion came from Belgrade. Note how the report omits exactly how the ICTY obtained the INTEL. The ICTY doesn't have any independent INTEL assets of its own. If the info came from a NATO source, we'd already have it w/o the ICTY pass trough. If the info came from Sarajevo, one could be darn sure there'd be some line in the story about how the nice guys in the Iztbegovic statelet were fighting terror........
Therefore, the only reasonable conclusion is that the INTEL came from one of the truckloads of documents Belgrade has submitted over the years to the ICTY exposing Mujhadeen terror.