Russian President Vladimir Putin. (Sergei Karpukhin / Pool/European Pressphoto Agency)

IT HAS been three months since Boris Nem­tsov, one of Russia’s leading opposition figures, was gunned down near the Kremlin in Moscow. Not surprisingly, those responsible for the brazen murder have not been identified, though a couple of alleged triggermen have been arrested. Mr. Nemtsov’s case joins a long list of unsolved political murders during the regime of Vladi­mir Putin, both within and outside of Russia. Some, including Mr. Nemtsov and the journalist Anna Politkovskaya, were gunned down on the street, while others were felled by exotic poisons — the former KGB operative Alexander Litvinenko, who died after ingesting polonium, a rare radioactive substance, in London.

It was consequently understandable that friends of the opposition activist Vladi­mir Kara- Murza sounded alarms after he suddenly collapsed in his Moscow office on Tuesday and was rushed to a hospital. Mr. Kara-Murza, who is just 33 years old, was variously reported in the subsequent hours to be suffering from double pneumonia, pancreatitis and kidney failure. His wife, who lives in Washington with their three children, told us that “there has not yet been a conclusive diagnosis, but there is a definite possibility of poisoning.” She said that his condition remained grave on Thursday and he had not regained consciousness.

Mr. Kara-Murza was a close associate of Mr. Nemtsov and other Russian opposition leaders and often accompanied them to meetings in Washington. While other dissidents fled the country under Mr. Putin’s mounting repression, the young activist bravely returned to Moscow to work as a coordinator for Open Russia, an organization sponsored by the exiled opposition leader Mikhail Khodorkovsky. His sudden illness came one day after the group screened a film about Ramzan Kadyrov, the sinister ruler of the republic of Chechnya and a close ally of Mr. Putin who is suspected of involvement in several political assassinations.

We’re in awe of the extraordinary resolve and fortitude of Russians such as Mr. Kara-Murza, who continue to document and call attention to the corruption and the criminality of the Putin regime even after so many others who did so have been murdered. But even more staggering is the complacency Western governments exhibit toward the crude attacks on peaceful opponents in a country that wishes to be, and often is, treated as a global power. Apart from North Korea, it’s hard to think of a nation where political murder is as much of a hazard as it is now in Russia. Yet Western leaders have said little about the slayings and go on treating Mr. Putin as if he were a civilized statesman and potential partner in solving problems such as Syria’s civil war.

We wish Mr. Kara-Murza a speedy recovery from whatever is ailing him; his family is seeking help from Israeli toxicologists and hopes to transfer him to a hospital outside the country. But it won’t be surprising if the cause of his collapse remains obscure — or just ambiguous enough to be ignored by those who do not wish to accept the truth about Russia’s murderous regime.