Mr Djindjic's move came with a price-tag - the collapse of the Yugoslav government.
But political leaders including Mr Djindjic and Mr Kostunica, have rejected her appeals so far.
Mr Djindjic's successor as prime minister, Zoran Zivkovic, has been mired in wrangling within his government.
In any event, the effects of Mr Djindjic's assassination are by no means over.
It was Mr Djindjic's allies in parliament who expelled the 21 DSS deputies on Tuesday.
Zoran Djindjic, Serbia's prime minister, said that he did not know where Mr Mladic was.
As the recent assassination of Serbia's Prime Minister Zoran Djindjic demonstrated, the Balkans will continue to be unstable, turbulent.
The defence is trying to show that Djindjic and his associates had a suspiciously close relationship with the gang.
Djindjic argued that international law required him to hand Milosevic over for trial.
At a news conference in Belgrade, a visibly shaken Interior Minister, Dusan Mihailovic, said the government would continue Mr Djindjic's reform programme.
In 2003 Zoran Djindjic, the then prime minister who was contemplating trying to deal with Kosovo in a realistic fashion, was assassinated.
Serbian Prime Minister Zoran Djindjic said the suspects - about 20 people - would be handed over to The Hague within three weeks.
Serbia's pro-Western Prime Minister, Zoran Djindjic, has been involved in an mounting power struggle with President Kostunica, a moderate nationalist, in recent months.
Milos Vasic, a Belgrade journalist and author of a best-selling book on the Djindjic killing, says he has been impressed by the court.
One of the few serious opposition politicians left, Zoran Djindjic, has had to flee to Montenegro, Serbia's rebellious little partner in rump Yugoslavia.
He had been convicted in absentia in 2007 of conspiring to kill Mr Djindjic, who was shot by a sniper in March 2003.
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Mr Djindjic said early elections were possible if the expulsions did not work and parliament could not function due to the lack of a quorum.
But correspondents say early elections would certainly not be in the interests of Mr Djindjic or his party, which has been lagging in the polls.
Mr Djindjic also stressed the need for urgent economic reform, saying Serbia was the last in Europe in terms of living standards, security, technology and infrastructure.
So a forum remains in which witnesses are claiming that Mr Kostunica and his allies helped to set the stage for the murder of Djindjic, his arch-rival.
"We have to be realistic and not to provoke new crises and new injustices and new war crimes by trying to deal with history and with old crimes, " Mr Djindjic said in London.
Mr Kostunica is said to be keen on the idea of early elections - a prospect made more real last week when Mr Djindjic's wing sacked 50 DSS MPs for failing to attend parliamentary debates.
So Zagreb does not need to take a legally questionable short-cut through the constitutional maze that Serbian Prime Minister Zoran Djindjic opted for when he transferred the former Yugoslav leader, Slobodan Milosevic, to The Hague last month.
When Milos Simovic shot (but failed to kill) Sretko Kalinic, it turned out that both belonged to Serbia's notorious Zemun gang, which had taken part in the assassination of Zoran Djindjic, the Serbian prime minister, in 2003.
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Mr Djindjic and Mr Kostunica and their respective parties joined forces in 2000 to oust former president Slobodan Milosevic, but have clashed over a range of issues, including economic and legal reforms, and co-operation with the international war crimes tribunal in The Hague.
Some more liberal figures likely to take posts in the new Serbian government say openly that suspects may indeed be sent abroad, while others, including a former senior policeman and a former general who both served under Mr Milosevic before siding with Mr Djindjic, disagree fiercely, for obvious reasons.
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