"Slobodan Praljak is not a war criminal. I am rejecting your verdict with contempt," Praljak shouted defiantly.
He then tilted his head back and drank from a small vial. As the judge appealed for him to sit down, Praljak declared: "I have taken poison."
The judge, looking disconcerted, suspended proceedings. The International Criminal Tribunal for the former Yugoslavia confirmed later Wednesday that Praljak had been given immediate medical help in the courtroom before being taken to the hospital, where he died.
Authorities in the Netherlands were on Thursday urgently investigating what the substance was and how Praljak was able to obtain it while being held in UN detention.
The dramatic courtroom scene unfolded as the work of the UN tribunal, set up to prosecute crimes committed during conflicts in the Balkans in the 1990s, came to a close after more than 20 years.
Wednesday's appeal hearing, which reaffirmed the sentences imposed in 2013 on Praljak and five other former Bosnian Croat leaders for crimes against humanity and war crimes and almost all their convictions, was the tribunal's final ruling and it will formally close at the end of the year.
Significantly, the appeal judges upheld the earlier trial's findings that implicated the Croatian regime under then-President Franjo Tudjman in a criminal conspiracy with the goal of "ethnic cleansing of the Muslim population" of parts of Bosnia to ensure Croatian domination.
The Bosnian Croat leadership, along with Croat leaders, wanted to make this territory part of a "Greater Croatia," the ICTY said when the case first went through the court.
Dutch authorities are now investigating the apparent security breach which allowed Praljak to take his own life. The ICTY said only that he had drunk "a liquid" and quickly fallen ill.
Croatian lawyer Goran Mikuličić told CNN's local affiliate N1 that "anyone could have brought him a bottle of poison easily." He said family, friends, journalists and lawyers were allowed to visit Praljak but that only lawyers were allowed to take bags into the detention facility.
Praljak isn't the first war criminal or suspect to kill himself while being held in the ICTY detention units.
Milan Babić, the president of the self-proclaimed "Serb Republic of Krajina" in Croatia, killed himself in 2006 after being convicted of crimes against humanity and war crimes against Croat civilians during the war in Croatia.
War crimes suspect Slavko Dokmanovic was found hanged in his cell in 1998 as he awaited the verdict in his trial.
Former Yugoslav leader Slobodan Milošević, who faced charges of genocide, crimes against humanity and other war crimes for his role in the conflicts in Bosnia and Herzegovina, Croatia and Kosovo, died in 2006 while on trial at The Hague.
The official investigation into his death confirmed that non-prescribed pills were found in his cell, but couldn't prove his intent to take his own life.
Edo Batlak, a former prisoner at one of the concentration camps the former Bosnian Croat leaders were convicted of creating, told N1 he believed Praljak's action was influenced by his pre-war role as a theater director.
"Praljak is a director by profession. So this aligns with his profession, he wants to be remembered by it," he said.
Praljak, who was detained in 2004, had already served two-thirds of his 20-year sentence, for offenses committed between 1992 and 1994, and would have been eligible for release in the coming months.
Despite being a convicted war criminal, Praljak still commands significant support in Croatia, in an indication of how the scars of the 1990s conflicts are yet to heal fully.
The Parliament of Croatia, or Sabor, began Thursday's session with a moment of silence to honor Praljak and all war victims.
The Parliament's President, Goran Jandroković, read a statement in which he said all parties represented in the chamber agreed that the verdict "does not honor historical truth, facts and proof" and as such was "unjust and unacceptable."
Representatives of the Social Democratic Party of Croatia and the liberal GLAS party, were not present for the minute of silence.
Croatia's Prime Minister, Andrej Plenkovic, had already offered his condolences and those of his government following news of Praljak's death.
Other Croat politicians also rejected the verdict.
Croatia's President Kolinda Grabar-Kitarović, who spoke Thursday after cutting short a state visit to Iceland, said: "His act struck the heart of the Croatian nation. Croatia was not the aggressor, but, along with the United States, did most for the unity of Bosnia and Herzegovina. Croatia and Bosnia were attacked by Milošević's Serbia and the Yugoslav National Army and those are facts. Croatia didn't attack anyone."
Dragan Čović, a Croat member of the Presidency of Bosnia, said: "We consider this (the verdict) primarily a crime against all honorable representatives of the Croat military forces and the Croat nation in Bosnia and Herzegovina."
About 1,000 Bosnian Croats gathered in a square in the southern Bosnian town of Mostar -- where some of the fiercest fighting occurred in the 1990s -- late on Wednesday to light candles in support of Praljak, Reuters news agency reported.
The other former Bosnian Croat leaders whose sentences were affirmed by the Appeals Chamber include Jadranko Prlić, prime minister of the self-proclaimed "Croat Republic of Herzeg-Bosnia," who was given 25 years in prison. Prlić led Croat separatists within Bosnia who wanted a part of Bosnia to be annexed to Croatia in collusion with Tudjman.
His niece, Lana Prlić, who is vice president of the Social Democratic Party of Bosnia, notably spoke out in support of the Hague tribunal in a statement on Facebook Wednesday morning.
"I respect and accept the verdict of the Court in the Hague," she wrote. "In our life, we have several families -- the one we choose and the one we are born into. The Social Democratic Party of Bosnia is my family that I chose as an activist in 2010. At the same time, I can't and don't want to escape the family whose surname I've carried since my birth in 1993. Everyone has to take responsibility for their crimes."
She called on politicians in Bosnia and Herzegovina and in Croatia to respect the court and also the victims of war crimes and their families, who had suffered for years.
Croat politician Goran Beus Richembergh, of GLAS, wrote on Facebook that he had received a number of death threats, including threats to kill his wife, after an earlier post in which he welcomed the verdict and called Praljak a lawfully convicted war criminal. Beus Richembergh said he had alerted the police.
He told Croatian TV channel Nova TV: "In the mass of insults I get every day for publicly taking a stand, I got threats that can be considered serious. Now the police have to solve it."
CNN has sought comment from the police in Zagreb.
According to the GLAS Facebook page, fellow party member Vesna Pusić, a former foreign minister of Croatia who also welcomed the verdict, has also received a death threat.