The suicide, in the detention centre at Schevingen jail, is a severe embarrassment for the Tribunal. Dokmanovic is the first Yugoslav war crimes suspect to die in custody. There are 27 more on, or awaiting, trial.
The Tribunal has 24 cells at its disposal at Schevingen, each 10 square yards in size and with its own bathroom.
While a prisoner is under close supervision the light in his cell burns continuously and a guard checks every 30 minutes. Dokmanovic turned off the light using an electric shaver to short-circuit the power supply.
The Tribunal and the Dutch police have both launched inquiries. Toma Fila, the Serb's lawyer, said: "He was psychologically disturbed. He believed in his innocence."
The death of Dokmanovic, arrested by a UN snatch squad exactly a year ago, brings the case against him to a close. "You can't pass judgement on a dead person," said tribunal spokesman Christian Chartier.
The ex-mayor was accused of having helped organise one of the most notorious massacres of the Balkan wars.
When Vukovar fell to Serb forces in November 1991, Yugoslav soldiers and Serb paramilitaries found about 420 wounded Croats in the local hospital. All but 60 were dragged from their beds, never to be seen alive again.
According to the prosecution, at least 200 patients, whose bodies have since been exhumed, were taken to a sheep farm at nearby Ovcara, beaten and then executed. As the Yugoslav soldiers and Serb paramilitaries marched into Vukovar they broke into a song dedicated to the Serb leader Slobodan Milosevic. "Slobo, bring the salad. There'll be meat, there'll be meat - we're cutting up the Croats," it went.
A Yugoslav Army officer, Veselin Sljivancanin, prevented Red Cross officials from entering the hospital while the wounded could be seen being taken out of the back.
Mr Dokmanovic's trial ended on Thursday last week, and the presiding judges had retired to consider their verdict.
He had pleaded not guilty, claiming he was nowhere near Ovcara at the time of the massacre. But Mr Dokmanovic's claim was undermined in testimony given to the court by a leading British tree expert.
Earlier, Dokmanovic's alibi had looked good. He said that in the hours running up to the massacre, on 20 November 1991, he had been leading a party of notables from an eastern Serbian town around the newly "liberated" city, and that a video with the date and time shown on screen would prove where he had been.
But last month the prosecutor, Clint Williamson, promised the court he would present "extensive evidence" to undermine this claim. His secret weapon was analysis by Paul Tabbush, who works for the Forestry Commission at Alice Holt in Surrey.
Mr Tabbush examined a mulberry, a walnut tree and a "distinctive Lombardy poplar", all visible on Dokmanovic's video. He was then sent to Vukovar where, having found the trees, he measured them.
After carrying out a comparative analysis he concluded Dokmanovic was not where he said he was at the time he had claimed.
This evidence was crucial - two survivors of the massacre said that in the hours before the killing started, Mr Dokmanovic had dropped in at the Ovcara farm and beaten up some of the prisoners. He denied this, but Mr Tabbush's testimony proved that it was possible.
In an interview, Mr Tabbush said: "Buildings get blown to pieces and traffic signs get knocked over by tanks, but trees retain their shape. As they grow, the angles of their branches don't change; they just get fatter."
He added that trees were unique and often easier to identify than humans because "people are symmetrical on a central axis whereas trees are not." Mr Tabbush's evidence was not enough to convict Dokmanovic of the massacre but it did destroy his alibi.
Of his visit to Vukovar, he commented: "We saw the exhumation of another site where there are some 1,300 people. Some had had their hands tied and been shot in the head."
On Sunday, 56 of these victims were reburied following a nine-week exhumation and reburial process which had turned up 938 bodies.
The International Criminal Tribunal for the Former Yugoslavia was set up by the UN in May 1993.
It is the first international body for the prosecution of war crimes since the Nuremberg and Tokyo trials after the Second World War.Reuse content