The body of Ivan Stambolic, the former Serb president and Slobodan Milosevic's mentor, was found buried in a wood yesterday, three years after he disappeared.
Mr Stambolic failed to return from a morning jog a month before a Yugoslavian presidential election, at which some expected him to challenge Milosevic. Police blamed his former protege for the murder.
The Serbian interior minister, Dusan Mihailovic, said Milosevic and his wife, Mira Markovic, were the key suspects and would be questioned soon.
"The investigation has established that Stambolic's execution was politically motivated," he said, describing the killing as "the greatest mystery of the former regime".
He said: "The aim was to remove Stambolic as a possible candidate in the presidential elections and this clearly shows who might have ordered his execution."
The abduction was carried one by four members of the elite police Unit for Special Operations, or JSO, which was set up under Milosevic. They had been arrested, Mr Mihailovic added.
"His remains have been dug out of a pit in Mount Fruska Gora," said Mr Mihailovic, referring to a national park 30 miles north of Belgrade. "He was executed with two shots and buried in a quicklime pit dug out in advance."
Members of the JSO, known as the Red Berets, killed the Serbian prime minister, Zoran Djindjic, this month. The unit has now been disbanded.
Serb authorities will ask the United Nations tribunal in The Hague, where Milosevic is being tried for crimes against humanity, for permission to question Milosevic in connection with Mr Stambolic's murder. His wife has not been seen since a big police sweep began after Mr Djindjic's assassination.
Mr Stambolic disappeared in August 2000, at a time when he deeply regretted taking Milosevic under his wing. He had taken to criticising the Serb leader, accusing him of destroying Serbia.
Mr Stambolic was one of the most prominent victims in a series of Mafia- style killings and kidnappings that marked the final years of Milosevic's decade in power.
In the event Milosevic lost the presidential vote to Vojislav Kostunica, and was toppled in a popular revolt after refusing to concede electoral defeat.
Mr Stambolic and Milosevic became close friends in the mid-1970s. Mr Stambolic, a powerful party leader in Tito's Yugoslavia, put the provincial Milosevic into his first position of power as the head of the Communist Party in Belgrade.
As Mr Stambolic climbed the political hierarchy, eventually reaching the Serb presidency, he pulled Milosevic up with him.
But in 1987, at the Eighth Party Congress, Milosevic stabbed his mentor in the back and staged a political coup. Milosevic's subsequent success represented the victory of Serb nationalism within the Communist Party.
The unscrupulous Milosevic then sidelined his former best friend, as Mr Stambolic gave warning of the dangers of nationalism.
Mr Stambolic's son said the discovery of his father's unmarked grave had offered the family some relief.
"I will finally be able to bury my father's body and light a candle at his grave," said Veljko Stambolic.