Prosecutors in Moscow have charged a powerful local politician from the restive North Caucasus region over the murder of an investigator.
Said Amirov, mayor of the city of Makhachkala in Dagestan, was arrested in a dramatic operation involving a helicopter and armoured vehicles.
He was flown to Moscow and charged along with two other men over the murder of an investigator in 2011.
He insisted he was innocent and said the case was politically motivated.
Mr Amirov and the two other suspects were formally charged with “encroachment on the life” of a law enforcement official, a crime for which they could be jailed for life.
They were also charged with circulating firearms illegally, for which they could be jailed for up to four years.
The charges relate to the murder of investigator Arsen Gadzhibekov, who was shot dead outside his home in the Dagestani town of Kaspiysk in December 2011. He was investigating criminal gangs at the time.
Dagestan is Russia’s most volatile region: criminal gangs and Islamist insurgents are active and there are almost daily shootings and bomb attacks.
Mr Amirov is a hugely powerful figure in the North Caucasus, the BBC’s Steve Rosenberg reports from Moscow.
He has been mayor of Makhachkala, one of Russia’s most dangerous cities, for the last 15 years.
In that time, he has survived 15 assassination attempts, earning himself the nickname “the immortal one”, although one attack did leave him partially paralysed and wheelchair-bound.
Only in April, Mr Amirov was named Russia’s most successful mayor.
During the arrest operation on Saturday, armoured personnel carriers blocked off streets around his house, then – according to witnesses – around 40 masked officers flown in specially from Moscow detained him.
The mayor was then flown by army helicopter to a jail in the Russian capital.