MOSCOW: Russian investigators on Friday charged ex-oil tycoon and Kremlin critic Mikhail Khodorkovsky with organizing the 1998 murder of a mayor in Siberia, ratcheting up their campaign against the exiled former Yukos boss.

“As a result of investigative work, we managed to obtain new information and in light of this, it was decided on Dec. 11, 2015, to prosecute Mikhail Khodorkovsky as a defendant for... the organization of murder,” Russia’s powerful Investigative Committee said in a statement.

Investigators announced in June that they were reopening a criminal probe into the 1998 murder of Vladimir Petukhov, the mayor of oil-producing Nefteyugansk city, saying that Khodorkovsky — then the head of the now-defunct oil giant Yukos — may have ordered the killing.

Former Yukos security chief, Alexei Pichugin, is already serving a life term for the mayor’s murder and investigators said Friday that “not one important decision was taken at Yukos without Khodorkovsky’s order.”

Khodorkovsky, who now lives in London, has claimed that the new probe into the mayor’s murder was ordered personally by President Vladimir Putin.

Once Russia’s richest man, he spent a decade in prison on charges of tax evasion, fraud and embezzlement, which he blames on a political vendetta by Putin.

In late 2013 he was unexpectedly released and flown out of the country after a presidential pardon. After intially pledging to stay out of politics, he has once again become an outspoken critic of Putin.

Khodorkovsky is also being charged with the attempted murders of Petukhov’s body guard, Vyacheslav Kokoshkin, and Yevgeny Rybin, the director of the Vienna-based East Petroleum Handelsges trading firm who survived two assassination attempts in 1998 and 1999, the statement said.

The Investigative Committee earlier this week had summoned the former oil tycoon for questioning and on Friday said that Khodorkovsky would be put on a wanted list “in the near future.”