And they were doing this from the very start. 99% of those in mass graves in Sarajevo have been, IDENTIFIED (keyword!) as Serbs. This includes many Serbs who were decapitated - and this was done by Balkan Muslims before the Mujahadeen came. I can also find reports which show Bosnian Muslim involvment in Croatia before the Bosnian war. A couple Bosnian Muslims accidently blew themselves up when they meant to attack Montenegro beach goers - that was August 1991.
http://www.newint.org/chronicle/CRONIC.HTM
BOSNIA Recently released secret documents reveal that in the first days of the war, Muslim paramilitary leaders murdered scores of Bosnian Serb civilians in Sarajevo.
According to our documentation, about 460 Serbs were killed in different parts of Sarajevo, including the outer suburbs Hrasnica, Tarcin, Pazaric etc. However, based on the number of the uninvestigated [mass graves] (these data are confirmed by the individuals close to the authorities and foreign organizations active in this field) the actual number is three times higher, at least 1,500. There are estimates that the actual number of victims is as high as 3,000...Unfortunately, "Kazani" is only one of the places where the corpses of the murdered people were hidden, if I can use that expression. Some of them were not Serbs, but 99 percent of them were. According to the information available to us, all together 30 corpses were found in "Kazani". Actually, 30 heads and 29 bodies. All the corpses were decapitated. However, murders occurred elsewhere as well...
Besides the infamous "Kazani" during the war corpses of the victims had been found in other parts of the city: in gutters, on the Trebevic bypass road, on the road to Pale, in Velesici, Pofalici, Brijesce, Buljakov Potok, Hrasno Brdo, Dobrinja... It is very important to mention that private prisons in which, according to certain evidence, murders of Serbs had taken place, were never investigated. As an example, I would like to mention prison "Stela" in Novi Grad, prison "Sunce" in Dobrinja, prison run by the then Fourth Motorized Brigade in Hrasnica, camp "Silos" in Tarcin and some other places.