Russian officials on Friday accused Mikhail Khodorkovsky, an exiled oil tycoon and former prisoner, of being involved in the 1998 killing of Vladimir Petukhov, a Siberian mayor, and in the attempted killing of businessman Yevgeny Rybin in 1999. Authorities had claimed before that they suspected Khodorkovsky's links to the killing, but did not have proof.

Khodorkovsky, the former chairman and CEO of the bankrupt oil and gas corporation Yukos, has so far denied the allegations by Russian prosecutors and, on Wednesday, accused Russian president Vladimir Putin of driving Russia to a point where a revolution will be "inevitable and necessary." He added that he will help to bring the revolution. He also accused Kremlin of conducting an "anti-constitutional coup" by following a suicidal foreign policy, introducing unlawful laws and prosecuting citizens in corrupt courts.

Petukhov was the mayor of Nefteyugansk, the town where Khodorkovsky's oil company was based at the time. In Rybin’s case, while the businessman survived an assassination attempt, his bodyguard was killed.

Khodorkovsky, who was once considered one of the richest men in Russia, was arrested in 2003 and charged with fraud in what has been previously referred to as an inquiry orchestrated by Kremlin. In May 2005, he was sentenced to nine years in jail over it and, in December 2010, while he was serving the sentence, his jail time was extended till 2014. He was pardoned by Putin in 2013, following which he moved to Switzerland.

Since his release, Khodorkovsky has openly criticized the Russian administration from Switzerland. Denying the murder allegations against him, Khodorkovsky said, according to Tass, that he was ready to face questions in the case, but only to Swiss authorities. He had also said Wednesday that neither he nor his representatives planned to appear in the Investigative Committee for questioning.

"If the country where I live not finds it necessary for me to answer these questions, I will do that," Khodorkovsky said, adding: "If the country where I’m now living deems it necessary to get answers to these questions [formulated by investigators], I’ll answer these questions."

He also said Wednesday, according to AP, that he told Putin in a pardon letter that he would not enter politics before his prison term ended and while he was taking care of his ailing mother. But since his mother passed away last August, he felt he "no longer had any obligations."