When it originally occurred, over a dozen witnesses on the ground stated they saw a "red streak" similar to a missile shooting up towards the plane immediately prior to the explosion. An early leaked/bogus news story stated that traces of PETN were found on the wreckage. LOTS of Stinger missiles were unaccounted for after the Afghan rebels we were covertly supporting finally convinced the Soviets to pull out. It is not implausible that it might have been one of those.