Reynaud Theunens said that Martic had written a report to Yugoslav People's Army (JNA) General Andrija Raseta saying that he had personally ordered the missile attacks on Zagreb.
The witness quoted reports by a JNA commission as saying that Martic and Serb paramilitary commander Milan Celeketic were to blame for the Serb defeat in the Western Slavonia region. The commission said that Martic made all decisions on his own and that Celeketic was preoccupied with politics rather than defence.
Those reports speak of the responsibility of Martic and Celeketic for the defeat in Western Slavonia and for the missile attacks on Zagreb, Theunens said.
Theunens cited a detail from Celeketic's letter of resignation to Martic, in which he said that he "acted in accordance with a doctrine of retaliation against vital targets on the opposite (Croatian) side."
At the time of the missile attacks, which were launched on 2 and 3 May 1995, Theunens served as a liaison officer of the UN Protection Force in Zagreb. He said that fires in and around the Croatian capital were a direct consequence of the cluster bomb attacks.
Martic, 60, is charged with 19 counts of persecution, extermination, killing and deportation of Croatian civilians in Serb-occupied areas of Croatia from 1991 to 1995, war crimes in Bosnia-Herzegovina in 1994, and missile attacks on Zagreb in May 1995.