ROBERT SIEGEL, HOST:

Russia's most prominent opposition leaders has been shot and killed. A Russian government statement says that gunmen shot Boris Nemtsov as he walked with a companion in central Moscow. President Putin has condemned the murder and called for an investigation. For more on this story, we're joined by NPR's Corey Flintoff in Moscow. And, Corey, what do we know beyond the barebones of the announcement about the shooting?

COREY FLINTOFF, BYLINE: So far, Robert, there's not very much. The authorities say Nemtsov was walking near the Kremlin with a woman companion. A white car pulled up, gunmen got out and shot him four times. The men escaped in the car, and as far as we know, there's no suspects in custody.

SIEGEL: Now, we know that Nemtsov was an outspoken critic of President Putin. What can you tell us about him as an opposition figure and as a politician?

FLINTOFF: He had a very promising career as a politician in the early 1990s. He was a political ally of President Boris Yeltsin. He supported Yeltsin through that 1991 coupe attempt by hardliners in the government. And then, Nemtsov made his name as a reformist governor in an important region near Moscow. And finally, he was named as a deputy prime minister in Yeltsin's government. He ran afoul of President Putin early in Putin's administration. And he's been an opposition figure pretty much ever since. He was a key organizer of demonstrations against Putin, and he was especially active in those massive demonstrations that took place back in 2011 and 2012.

SIEGEL: Now, Corey, opposition parties in Russia have gotten progressively weaker since then. Has Nemtsov had a big role in the last couple of years?

FLINTOFF: Well, given that the government has severely repressed most opposition activity, he hasn't been as prominent lately. He was very active, though, as kind of gadfly, basically trying to expose what he said was massive corruption in Putin's government and Putin's inner circle. For instance, Nemtsov published a pamphlet alleging that Putin's associates stole tens of billions of dollars during the construction of the Winter Olympic Games in Sochi. Nemtsov was from Sochi, himself. He actually ran for mayor there. In this pamphlet, he did very basic arithmetic with the budget for the games, and he challenged the government to explain these sums that weren't accounted for.

SIEGEL: He was also at odds with the Kremlin on the conflict with Ukraine, wasn't he?

FLINTOFF: Yes, he was among the very few Russian politicians who openly opposed Russia's annexation of Crimea. He said the peninsula was an integral part of Ukraine and that the annexation was illegal. And that of course is a position that went very strongly against Russian popular opinion, but he was undaunted about saying so.

SIEGEL: That's NPR's Corey Flintoff reporting on the shooting death of Russian opposition leader Boris Nemtsov. Corey, thank you.

FLINTOFF: Thank you, Robert. Transcript provided by NPR, Copyright NPR.