The Hague: A UN tribunal that was stunned by the courtroom suicide of a Bosnian Croat war criminal said on Thursday it was working with Dutch investigators to piece together how he smuggled a fatal dose of poison into the high-security building.

Slobodan Praljak, 72, died on Wednesday at a hospital in The Hague within hours of drinking a vial of liquid during the reading of his appeals judgment at the International Criminal Tribunal for the Former Yugoslavia.

Preliminary testing confirmed that the cause of death was "drinking a liquid that can kill," spokesman Vincent Veenman of the public prosecutors office in The Hague said. "We cannot yet say what that substance was. Further testing is needed," he said.

A 5-member ICTY appeals bench upheld Praljak's conviction on charges of crimes against humanity over persecution, murders and expulsions of Bosnian Muslims from territory captured by nationalist Bosnian Croats and the brutal imprisonment of wartime detainees. Reuters