The lead investigator into Voronenkov’s murder was Pavlo Kononenko, deputy prosecutor for Kiev. Kononenko could watch Russian television and read the country’s press, which contained myriad articles about Voronenkov’s life in Moscow, but diplomatic relations between the two countries have ceased and he could not question anyone there. Voronenkov had become an object of fascination in his own country — trashy programs looped on prime-time television, speculating on his career, the insincerity of his marriage to Maksakova and the involvement of the C.I.A. or its Ukrainian analogue, the S.B.U., in a setup. Television presenters interviewed guests who were sure that Voronenkov had undergone plastic surgery and was alive and well in Tel Aviv.

When I met Kononenko in his downtown office, he walked me through his investigation. He was focused on the gunman and his accomplices — right-wing ultranationalists who lived in a constellation of ramshackle towns in central Ukraine. Since 2016, Ukraine had experienced a surge of unexplained deaths, nearly a dozen in all, and Kiev had come to feel like a city of assassins in waiting. Ukraine immediately blamed Moscow for all the murders, but none were definitively linked to the Kremlin; most remain unsolved. Russian media outlets used the incidents to portray Ukraine as a warning of what happens to a nation when masses mobilize: instability, chaos and right-wing fanatics terrorizing citizens in the streets. Ukraine, meanwhile, saw the killings as more evidence of Russia terrorizing its population, after centuries of oppression and the recent war in Ukraine’s east, which has killed more than 10,000 people.

A large Ukrainian flag hung in one corner of Kononenko’s office, while the country’s coat of arms — a gold trident on an azure background — was mounted on the wall above his neatly arranged desk. He covered the table between us in charts, photographs and stills from surveillance footage of the assassin and his accomplices moving through Kiev. “We analyzed around three terabytes of information received from video control cameras and mobile-phone connection traffic,” he said. The S.B.U. tapped its network of informers. “Everyone worked with their agents, developing connections of our potential persons involved, trying to understand. Who could prompt them to perform this crime? Who could have been the customer? Who could have been assisting them?”

Kononenko assured me that he had done his best to comb through Voronenkov’s life despite the obstacles presented to him. Before he was murdered, Voronenkov had offered his own theories about who might want him dead. In his Interpol filing, he wrote that as a member of the Federal Drug Control Service, the F.S.K.N., Russia’s equivalent of the D.E.A., he led an investigative unit that helped crack a sprawling corruption case known as Three Whales, which has been called “the criminal case of the Vladimir Putin era.” More than a dozen high-ranking officials, including F.S.B. generals, were dismissed as a result of the investigation. Voronenkov said that the security services retaliated against him; in particular, he claimed that his work had drawn the ire of a notorious F.S.B. general named Oleg Feoktistov, who was known in Russia for his involvement in cases that brought down prominent officials. Feoktistov’s mentor was dislodged in the raid, and Voronenkov said Feoktistov pledged vengeance. In the end, it was the general’s plot, according to Voronenkov, that cost him his homeland and forced him to Ukraine.

By the time I met with Kononenko, I had been to Moscow in search of facts about Voronenkov, while well aware that they might be difficult to find; even if they did exist, I was certain I would find only shards of them. I spoke to Russian officials, lawmakers in the Duma, lawyers, businessmen and former security service officers. Few were eager to sit down with me. As one former security service member put it: “Unlike you, we live in a country where you can get seriously hurt for words. It is one thing for you to get a correct image, and it is another thing for me to spoil my life.”

Nearly everyone said Voronenkov was not the man he claimed to be. With uncanny regularity, they compared him to a fictional character in satirical Russian literature named Ostap Bender, a charlatan who traveled the country fleecing unsuspecting victims, seeking a score big enough to flee to Brazil. “Just show me a rich person, and I’ll take his money from him,” Bender tells a protégé. “I personally know 400 relatively honest methods of taking money. That’s not a problem.” While Bender had exposed the idiocies of Communist policy, Voronenkov’s tale, to those who know contemporary Russia, illuminated the chaos of Putin’s sistema: the personal rivalries, criminals, elites, crooks and clans trying to keep from running afoul of the country’s ever-shifting red lines. “It’s an absolutely unimaginable biography, even for Russia,” said Andrei Kolesnikov of the Carnegie Moscow Center, shaking his head at the information I presented him. “It means he was in the center of different kinds of communications — the mixture of criminal activity and state activity.”