Denis Voronenkov / Photo from UNIAN

It was Feoktistov who initially leaked information which became the base for an investigation by Russian opposition’s Alexei Navalny, against Russian Prime Dmitry Medvedev, Ponomarev said in an interview with Apostrophe.

"It is important that Feoktistov was the source of information, and Medvedev managed to prove it to Putin. So Putin ordered Sechin [Rosneft CEO] to sack Feoktistov from his position, and Sechin dismissed Feoktistov from office in February," Ponomarev said.

That is why Feoktistov remained an FSB general with operational capabilities, but without an office. In this situation, apparently, he remembered his "favorite" foe, Mr Voronenkov, because it was back in that February when a scandal erupted with his testimony in the Yanukovych case.

"It was such a big high-profile scandal. So, this man [Voronenkov] changed his status from being a personal enemy of Feoktistov to the enemy of the state, as a defector who had to be punished under Mafia laws," the former Russian deputy believes.

Read alsoRussian Duma's ex-deputy Voronenkov shot dead in Kyiv (Photos)"I think that this is exactly what the scenario was–ultimately to get back to active service, or at least to secure an indult forever. However, I still have one small question: Did Feoktistov call Putin before or after the murder?" he stressed.

Ponomarev went on to say that it’s ultimately Putin bears responsibility for the murder. That’s because he created the system, allowing such people remain politically untouchable.

The former State Duma deputy said that Voronenkov had known a great deal about financial interests of top security service officials. While he was part of the law enforcement system, he became famous for the so-called "Three Whales" multi-billion smuggling case. 

"Billions of dollars were at stake, and top FSB generals were beneficiaries. As a result, 29 FSB generals were sacked, that’s the entire top of the agency’s economic bloc. This was back in the early 2000s. Since then, he has become a personal foe of the FSB," Ponomarev emphasized.

Read alsoThe Washington Post remembers 10 Putin critics who died violently or in suspicious waysAs UNIAN reported, Voronenkov was assassinated downtown Kyiv on the morning of March 23. His bodyguard was wounded but managed to shoot back and hit the attacker, who later died of wounds at a Kyiv hospital.