Alexander Yurevich Borodai claimed over the weekend that he had in possession what he believed to be the black boxes of the downed Malaysia Airlines Flight MH17.
"We have found some technical parts," Borodai said in a press release on Sunday.
"We assume that they are black boxes. We do not have aviation experts and that is why we cannot state precisely that they are. Those parts have been delivered to Donetsk and they are under my control. We are waiting for experts to pass on the stuff."
While the devices have so far not been seen by anyone, Borodai, the self-proclaimed prime minister of the so-called Donetsk People's Republic, has certainly caught the eye of the international media.
Since Flight MH17 crashed into the eastern Ukrainian town of Grabovo, about 90 minutes from Donetsk, killing all 298 onboard last Thursday, Borodai has been the face of pro-Russian separatists fighting for independence from Ukraine.
Borodai might not have expected such attention either. Not too long ago, he was just an ordinary guy working as a consultant for an investment fund in Moscow.
But nowadays, the fast-talking Muscovite with a stylish goatee commands what he says are hundreds of fighters from Russia, according to a New York Times report in May.
Borodai, who has a degree in philosophy from Moscow State University, was appointed to the post by the republic's Supreme Council on May 16.
The Russian citizen says he came to eastern Ukraine out of a surge of patriotism and a desire to help Russian speakers there protect their rights.
But he has no connection with the Kremlin, he insists.
"I'm an ordinary citizen of Russia, not a government worker," said Borodai, who turns 42 this week.
"A lot of people from Russia are coming to help these people. I am one of them," he was quoted as saying.
To many, Borodai may seem to have come out of nowhere. But in Russia, he is a known quantity, according to New York Times.
He comes from a group of ultranationalists who were part of the far-right Zavtra newspaper in the 1990s. Their Pan-Slavic ideas, aiming for the unity of Slavic peoples, were considered marginal at the time, New York Times reported.
But they have now moved into the mainstream, helping formulate the worldview of today's Kremlin, said Oleg Kashin, a Russian investigative journalist who has written extensively about Borodai.
"He's the Karl Rove of Russian imperialism," said Irena Chalupa, a fellow at the Atlantic Council.
Borodai declined to say how many black boxes had been found and declined to disclose their colour (they are usually bright orange for easy detection).
Borodai said he will hand over the black boxes to the International Civil Aviation Organisation once they arrive at the region.
Of the Ukrainian authorities, Borodai said: "We don't trust them, as they may tamper with the devices, swap them and prevent investigation."
Besides the "black boxes", Borodai's men also removed some of the bodies of passengers aboard the downed Malaysia Airlines jet from the crash site.
They did this to be "humane", the rebel leader told NBC News.
He refuted reports that his forces forced emergency workers at gunpoint to hand over 196 bodies recovered from the crash site and then had them loaded onto refrigerated train cars.
Borodai, who is among the rebel leaders who had travel bans and asset freezes imposed by the European Union earlier this month, insisted his forces were acting compassionately.
"We have already refused to wait for the experts and had to start clearing the bodies from the scene of the event, because waiting longer was contradictory to what it means to be humane," he said.
When asked by NBC News whether he was in contact with Russian authorities, Borodai replied: "Officially, no." Unofficially? "No comment," he said.