Okun, a witness for the prosecution, served as a deputy to Cyrus Vance, the personal envoy of the UN Secretary-General for the former Yugoslavia, in 1991/92. He described how during their visit to Vukovar Major Sljivancanin used lies and threats to prevent them from visiting the hospital where hundreds of wounded people and civilians were waiting to be evacuated from the destroyed and besieged city.
Okun said that on the morning of 19 November 1991 he and Vance were taken to Vukovar from Belgrade in JNA armoured personnel carriers, but that upon arriving in the city they were stopped by Sljivancanin at a bridge en route to the city hospital.
Sljivancanin said that the bridge was mined and dangerous and that we could not go to the hospital, but we could see vehicles crossing the bridge, said Okun, whose testimony was accompanied by a TV recording of the conversation between Vance and Sljivancanin, showing scenes of the destroyed city.
Vance repeated his request to visit the hospital several times and eventually tried to proceed to the hospital, but Sljivancanin raised his rifle, pointing it at him and shouting, Okun said.
Prosecutor Marks Moore questioned Okun about entries from a logbook which the US diplomat kept at the time.
Retired JNA General Mile Mrksic, Major Veselin Sljivancanin and Captain Miroslav Radic are standing trial for crimes committed against at least 264 wounded people and civilians taken from the Vukovar Hospital and killed at the Ovcara farm outside the town on 20 November 1991.
The witness said that on 19 November they visited the JNA barracks in Vukovar, where they were able to see that the building was almost intact, although Sljivancanin claimed that it had been hit with 400-500 shells every day, which prompted the JNA to attack Vukovar.
Vukovar looked horrible, almost every building was destroyed, Okun said.
Herbert Okun in February 2003 testified at the trial of former Yugoslav president Slobodan Milosevic and was also a witness for the prosecution at the trial of Bosnian Serb leader Momcilo Krajisnik.