Russia's security service says it paid a $10m (£5.2m) bounty for information that led to the killing of Chechen rebel leader Aslan Maskhadov.
Russia blamed Maskhadov for a series of attacks
The service "was approached by certain citizens who gave the necessary information" on his whereabouts, the agency said in a statement.
The Russians said Maskhadov was killed last week in Chechnya, when troops found a bunker where he was hiding.
Russia offered a $10m reward for his capture in 2004.
Moscow blamed Maskhadov for a string of deadly attacks in Russia, including a rebel attack on a school in the North Ossetian town of Beslan last September in which more than 330 hostages - half of them children - died.
Maskhadov, who advocated negotiations to end the conflict between Chechen separatists and pro-Moscow forces, said he was not involved.
The authorities have refused to hand over Maskhadov's body to his family because of a Russian law which says terrorists can be buried in unmarked graves.
The security agency did not say who or how many people had provided the information.
However, a spokesman suggested there was more than one informant.
"These citizens were paid the monetary reward in full, if necessary they will receive help in moving to another Russian region or a Muslim country," he was quoted as saying by AFP.
The spokesman said the federal security agency, the FSB, was "ready in the future to assure the personal security and payment of any appropriate rewards to citizens who provide reliable information about the whereabouts of terrorist leaders".
Andrei Piontkovsky, director of the Centre for Strategic Research in Moscow, told the BBC News website that divisions within the Chechen movement meant Russian security forces could find it easier to recruit informants.
"This was most probably a case of betrayal" by forces close to Maskhadov, he said.
However, the BBC's Russian affairs analyst Steven Eke cautioned that the details surrounding the payment of the reward were suspicious - that the sum of money said to have been paid was unprecedented, and the official explanation of the events leading to Maskhadov's death was not clear.
Russian forces hailed Maskhadov's killing as a significant blow against Chechnya's rebels.
However, many in the Russian media have questioned the official version of his death.
Reporters who visited the scene said he may not have been cornered in an underground bunker as officials claim, but rather captured elsewhere, possibly interrogated, and then his body brought to site.
On Sunday, however, Russian security forces demolished the bunker and a house above it saying they feared there were booby traps.
Human rights campaigners say the move has helped destroy evidence that may have contradicted the official story.
"There is nothing left now to question the official version of events," prominent journalist Anna Politkovskaya told the Associated Press news agency.
Maskhadov, 53, was elected Chechen president in January 1997 but was ousted two years later.
He led the Chechen separatists who defeated Russian forces in a 1994-1996 war.