The prosecutor’s office denied that Mr. Herman worked for Ukrainian counterintelligence.
In Moscow, Dmitri S. Peskov, the spokesman for Mr. Putin, said on Friday that the Kremlin had nothing to do with the operation.
“No such foundation exists in Russia,” he told reporters. “Any allegations about Russia’s possible complicity in this staging is just mudslinging. They do not correspond to reality.”
Ukraine faced continued criticism from international organizations, foreign political leaders and journalists for faking the assassination, which they said had validated the Kremlin’s all-purpose claim that it is falsely blamed for every evil in the world by a “Russophobic” West.
Aside from hinting that catching the organizer hinged on completing the killing, Ukraine has not made it clear why such a deception was necessary. Nor has it provided any evidence about accomplices or a coherent time line. Officials said the ruse was two months in the planning stages.
The level of international criticism was such that the Ukrainian Embassy in London felt compelled to issue a statement justifying what it called a “special operation.” “The hybrid war waged by the Russian Federation against Ukraine demands unorthodox approaches,” it said.
For his part, Mr. Babchenko said he was not privy to all the details of the investigation, but went along with the ruse because he believed his life was at risk. Numerous other critics of the Kremlin who have gone into exile in Ukraine have been murdered on the streets of Kiev, the Ukrainian capital, previously.
“They probably had their reasons,” he said of the security services at a news conference on Thursday. “Maybe they wanted to collect proof that was 100 percent solid.”