In the 10 days that have passed since Alexander Litvinenko, an ex-KGB agent, died of radiation poisoning in London, we have learned a lot about his death — haven't we?

Well, we have learned that Litvinenko died after somehow ingesting polonium-210, a relatively rare radioactive substance. We have learned that a mysterious Italian, Mario Scaramella — a self-employed "security expert" who last year claimed that he'd found ex-KGB men selling nuclear material in the postage-stamp republic of San Marino — has been poisoned. We have learned that various other ex-KGB agents floating around London also have tested positive for polonium-210, as have a Piccadilly sushi restaurant, a London hotel room and a few airplanes.

We have learned that Litvinenko may or may not have known who murdered the Russian journalist Anna Politkovskaya earlier this year (and that the same people may have killed him); that he may or may not have been involved in a scam to blackmail various prominent Russians (unless that's just information planted in the British press); that he may or may not have possessed a dossier proving that the Kremlin framed the imprisoned billionaire boss of the Yukos oil company, Mikhail Khodorkovsky (unless that's what Khodorkovsky's people, or some other people, want us to think); that he may or may not have possessed proof that Vladimir Putin — another ex-KGB officer, now president of Russia — ordered his goons to blow up some apartment buildings in Moscow several years ago, a terrorist act that launched the current Chechen war.

In other words: Though we don't know who killed Litvinenko, we have learned that London is a more exciting place than we thought it was. We have learned that the complex plots of Dostoyevsky novels merely reflect Russian reality. And we have learned that the old KGB lives on in new guises.

Or rather, we have been reminded that the old KGB lives on in new guises. True, the old employees no longer belong to a single all-powerful institution. Some ("the stupidest," according to Oleg Gordievsky, the former double agent) have stayed with the agency, joining either the domestic service (FSB) or the foreign intelligence bureau (SVR). Others went into business, some joining the security entourages of new Russian millionaires, some becoming Russian millionaires in their own right. Still others, to put it bluntly, went into organized crime. And some — President Putin is the shining example here — went into politics.

Despite their widely varying fates, it has long been clear that many of these old comrades continue to work together in mutually profitable ways. As far back as 1999, for example, a group of Russian-born bankers was caught laundering money through a New York bank, probably using information obtained, one way or another, by Russian intelligence. Since then it has become clear that a number of Russia's largest companies were launched with money from mysterious sources, and a number of former KGB officers have shown up at the helm of businesses and banks, too.

This same mutually profitable relationship will also make it extremely difficult to find Litvinenko's real killer. After all, this set of post-KGB relationships is nothing if not complex: There are conspiracies within conspiracies, agents of agents of agents, people who pretend to be acting on behalf of a particular oligarch or Chechen insurgent who are actually acting on behalf of someone quite different. It is possible that Litvinenko was murdered by "rogue secret policemen," as the British press suspects. It is also possible that the "rogue secret policemen" were working for someone who worked for the Kremlin, or someone who worked for a Russian oligarch, or who worked for a Russian oligarch who worked for the Kremlin.

As the investigation progresses, I'm sure many more wonderfully shady characters will emerge, along with many theories about who was trying to discredit whom. But though it's doubtful that he ever gave an actual order to an actual thug, Putin is certainly responsible for Litvinenko's death in this deeper sense: He presides over this web of old intelligence operatives, indeed, sits at its center. And he approves of their methods.

One of his first acts as prime minister in 1999 was the unveiling of a plaque to Yuri Andropov, the former KGB boss best known for his harsh treatment of dissidents. No one should have been surprised that the former KGB's harassment of modern "dissidents" grew harsher with every passing year — or that it culminated in this strange murder.

That we were surprised, are surprised, is both tragic and ironic: After all, for the better part of a decade now, we've been desperately looking for weapons of mass destruction and for the strange new enemies, the Islamic radicals who might be planning to use them. And now we've discovered that there really is nuclear material for sale and that it really is being used, in the West, to kill people. And that the killers aren't strange, or new, or even Islamic.

Anne Applebaum is a columnist for the Washington Post.