PARIS — The moment was dramatic enough: In a courtroom in The Hague on Wednesday, a military commander from the former Yugoslavia pulled out a small bottle and drank from it, declaring that he had ingested poison to protest his conviction for war crimes. The judges quickly ordered that courtroom curtains block the view of spectators in the public gallery. Live television coverage went dark.

But what happened next, beyond public view, was just as shocking, according to lawyers and court officials. The war criminal, Slobodan Praljak, 72, slumped in his chair and began to gasp for breath. He was later taken to a Dutch hospital and pronounced dead.

On Friday, Dutch prosecutors announced that Mr. Praljak had died of heart failure after ingesting potassium cyanide — a highly toxic compound — and the International Criminal Tribunal for the Former Yugoslavia announced that it would conduct its own “independent, expert review” of Mr. Praljak’s suicide. But a key question remained unanswered: How did he manage to smuggle the poison into court?

Defense lawyers at the tribunal say the security arrangements in place for defendants like Mr. Praljak, and the five other men whose sentences were affirmed on Wednesday, were rigorous. They were subjected to body searches when they left their detention center — inside a high-security Dutch prison — and again when they arrived at the tribunal building. But, lawyers acknowledged, body-cavity searches were not part of the routine.