Once a close associate of Slobodan Milosevic, president of the former Yugoslavia, Babic was considered an ''insider" with special knowledge of the workings of Milosevic's regime, and prosecutors put him on the stand for three weeks of dramatic testimony against his former mentor in 2002.
His death will be a setback for UN prosecutors who had planned to summon him as a witness in as many as three more war crimes cases. He had agreed to testify against his former comrades as part of a plea bargain.
Babic, 50, who was sentenced in 2004 to 13 years' imprisonment, was found dead at 6:30 p.m. at the UN detention center in Scheveningen, a few miles from the war crimes tribunal in The Hague.
His body was discovered during a routine half-hourly monitoring of his cell, tribunal spokeswoman Alexandra Milenov said.
''He gave no indication he was contemplating such a move," Milenov said. ''There was nothing unusual in his demeanor."
The tribunal said it was launching an inquiry.
His was the second suicide at the detention unit, following the 1998 death of Slavko Dokmanovic, another Croatian Serb leader.
Rasim Ljajic, chief of Serbia-Montenegro's government agency for cooperation with The Hague tribunal, said Babic's death probably would deepen the distrust most Serbs have for the UN tribunal, created in 1993 to try those responsible for massacres and atrocities being committed during Yugoslavia's violent breakup.
''This second case of suicide certainly won't help our public's perception about the tribunal," he said.
The Association of Serbs from the Croatian Krajina, a Belgrade-based group, said Babic's suicide indicated that the tribunal ''obtains its confessions through extraordinary pressures and lies," and that Babic ''resorted to the only solution he could in defense of human dignity."
Babic, a former dentist, was a ranking Croatian Serb leader when the Serb minority revolted after Croatia declared independence from Yugoslavia in 1991, setting off a war that lasted until 1995.
Babic was accused, along with Milosevic, of being part of a conspiracy to clear roughly one-third of Croatia of non-Serbs and incorporate that area into an ethnically pure Serbian state.
