Police have found the grave of a missing former Serbian president they believe was killed by an elite police unit also suspected in the slaying of Prime Minister Zoran Djindjic, authorities said Friday.

The announcement came less than a day after two main suspects in Djindjic's assassination died in a shootout with police. Investigators believe Dusan Spasojevic, 35, and Mile Lukovic, 34, were leaders of the Zemun Clan, a crime gang with ties to former President Slobodan Milosevic that allegedly arranged the killing along with the police unit.

The gang members had been hiding for days in the Belgrade suburb of Barajevo, authorities said. As officers tried to arrest them Thursday night, they "opened automatic fire, forcing the officers to respond," police said in a statement Friday.

The government did not specify what role the two allegedly played in the assassination. A police official speaking on condition of anonymity said they organized and financed the plot.

On Friday, Interior Minister Dusan Mihajlovic said police had found the body of Ivan Stambolic, Serbia's president in the late 1980s, in a lime-covered grave on a mountain in northern Serbia.

Stambolic, a bitter foe of Milosevic, had been missing since August 2000, when when he was abducted by unknown assailants while jogging in a Belgrade park.

It was believed that Milosevic ordered him killed because of fears he might have run against him in Yugoslav presidential elections in October that year. Milosevic eventually lost that vote to Vojislav Kostunica, and was toppled in a popular revolt after refusing to concede defeat.

Mihajlovic blamed four members of a special police unit loyal to Milosevic for the murder and said they had been arrested.

The interior minister told a news conference an investigation has shown that the motive for Stambolic's murder was political.

Police planned to interrogate Milosevic -- who is on trial at the U.N. war crimes tribunal in The Hague, Netherlands -- and his influential wife Mirjana Markovic in connection with the Stambolic's grave, he added.

Stambolic's son Veljko told The Associated Press that the unmarked grave was discovered on Thursday.

"I will finally be able to bury my father's body and light a candle at his grave," Veljko Stambolic said.

The police unit, known as Special Operations Unit, was disbanded Wednesday after several of its members were arrested on charges they were linked to Djindjic's assassination as he stepped from his armored car in downtown Belgrade.

Authorities did not elaborate Friday on the specific role Spasojevic and Lukovic played in Djindjic's assassination, but a ranking police officer, speaking on condition of anonymity, said they were "directly involved in the plot to kill Djindjic, they organized it, they financed it."

Police have rounded up more than 3,000 suspects in the investigation that followed the assassination. About a third of them remain in custody.

Earlier Thursday, about 15 members of the elite police unit were detained on suspicion they helped organize the assassination.

Police on Monday arrested Zvezdan Jovanovic, accused of firing the shots that killed Djindjic who was ambushed as he left an armored car outside the government building in Belgrade. Jovanovic, the special police unit's deputy commander, served as Milosevic's bodyguard before he was ousted in a Djindjic-led popular revolt in 2000.

The group's ringleader, Milorad Lukovic, known as Legija, who also served as the special unit's commander, remains at large. He is not related to Mile Lukovic, the killed suspect.

Milosevic's regime forged ties between paramilitaries and drug-dealing gangs which continued even after democratic leadership took over.

As president, Milosevic allowed underworld figures to fight with notorious paramilitary units in the Balkan wars of the 1990s. Afterward, he gave them a free hand to join regular police forces such as the special unit, authorities say.

Djindjic engineered Milosevic's extradition to the Netherlands-based U.N. tribunal where the former president is on trial for genocide and other war crimes stemming from the wars in Croatia, Bosnia and Kosovo. Afterward, Djindjic spearheaded efforts to crack down on the underworld, which made him many enemies.