Here is just some testimony from the Hague. You will note that the Muslims already had heavy weapons in late 1992 and there were military battles causing casualties on both sides. The media presented it as Serbs suddenly firing upon civilians, when they were acting against the Muslim militants.
Further, a witness says that the days often started quiet until the Muslims would launch mortar attacks at 6:00 a.m., and the Serbs would fire a greater number in response. What else could they do?
http://www.un.org/icty/transe29/020524ED.htm
WITNESS: JAMES PHILIPE CUTLER
“...I flew into Sarajevo as a senior military observer on the 21st of December, 1992, and officially took over from Lieutenant-Colonel Richard Mole on the day after Christmas, [Realtime transcript read in error " "] the 26th of December, 1992.
Yes, I have covered the -- to monitor the airport agreement, to monitor the heavy weapons concentration sites on both sides, to monitor prisoner of war and body exchanges, to monitor the incoming and outgoing fire on both sides, and from the main mandate, to provide our best humanitarian efforts anywhere we could and to generally report the situation as it was reported by UNMOs so that those reports would go through to high headquarters. Those were the major tasks…
A. Just prior to me arriving in Sarajevo, there was what Colonel Mole described the battle of Otes, which was on the western flank of Sarajevo city. There had been intense battle, preceded by heavy artillery concentrations, tank fire, anti-aircraft fire, and very intense front line infantry attacks. The front lines in that particular area were very close. Colonel Mole told me that I had arrived at a good time because they were licking their wounds and removing bodies from the battle site. And a total evidence would indicate there was many casualties on both sides, and once again, anecdotal evidence would indicate it was a time when the Bosnian Serb Army, the Sarajevo Corps, realised that there was some very strong resistance, and I think there was a lot of loss of life on the front lines on both sides.
…It disturbed me greatly that it would appear that both sides had great delight on sniping of UNMO vehicles, on UNMO OPs, and also there had been the odd close shelling to UNMO OPs within Sarajevo.
Q. Colonel Cutler, during the course of your tenure in Sarajevo, do you -- or did you receive any information that the army of Bosnia-Herzegovina was using the hospital grounds to launch mortars?
A. Yes, there had been a lot of rumours floating around that, in fact, mortars were being used or various United Nations installations, the locations of the Egyptian and Ukrainian battalion, and in particular, the Kosevo hospital had been used to screen firing of mortars by the Presidency forces.
On the -- I was obviously delighted that on the second week in January, I think it was on the 12th of January, a colonel sergeant from the British Cheshire regiment, who had been in charge of mortars, asked to see me. He had been asking who he could give a statement to. I welcomed him into my office and I took a statement from him that involved him witnessing the fire of a mortar, an 82-millimetre mortar, from adjacent to the Kosevo hospital. I think it was early afternoon. The Colonel sergeant had been escorting a convoy of fuel to that hospital. He and his crew observed this mortar firing five rounds from the hospital, adjacent to the hospital grounds, as part of the hospital grounds.… On leaving the hospital grounds, which would have been in the order of 30 minutes later, the hospital came under mortar, artillery, and anti-aircraft fire…
In the February-March period, that was – seemed to be particularly evident to the stage where we would get up in the morning, 6.00, no activity whatsoever and then we would hear a couple of "pop pops" which were obviously outgoing mortar fire from the Bosnian, and within a short few minutes later, there would be incoming fire, and normally the incoming fire would be more than two rounds. If two rounds were fired out, it would be something in the order of 10 to 15 rounds would be incoming…
So you would hear outgoing fire from the Presidency side, the Bosnian side, followed by incoming?
A. Correct.