The man I met on a street in London’s Mayfair district back in the summer of 2002 looked younger than his thirty-nine years. He was wearing sunglasses and a casual open-necked shirt, and a gold cross dangled from a chain draped around his neck. His blond hair, closely cropped in the photographs I had seen of him, spilled untidily over his collar. Alexander Litvinenko, in short, did not fit the picture I had in mind of a former lieutenant-colonel in the Russian Federal Security Service (FSB), the successor agency to the KGB.

Litvinenko, as is now known by all the world’s followers of this James Bond-like tale, died recently in London from poisoning by polonium 210, a radioactive isotope. The poison invaded his gastrointestinal tract and spread through his body, causing severe pain and the loss of his hair. Scotland Yard has declared his death a murder. But ordered by...? And what was the motive? On his deathbed, Litvinenko dictated a statement baldly accusing Russian President (and former KGB colonel) Vladimir V. Putin of the deed. But his words to Putin—“you have shown yourself to be as barbaric and ruthless as your most hostile critics have claimed”—sounded less like a measured criminal indictment than a scripted political tract.

I had at best a hazy recollection of my one and only encounter with Litvinenko. But I tend to be a saver, and in a cardboard box jammed into a closet at home I found a prize: Ten pages of hand-scrawled notes of our interview. As I read over them, I came across this line: “England is a very safe country. But these people we’re talking about”—he meant his ex-colleagues in the security services—“are capable of anything.”

Our meeting was incidental to my main purpose in London—to interview Boris Berezovsky, a notorious Russian billionaire oligarch who had fled to the U.K. after a bitter falling out with Putin, whom he had helped install in the Kremlin. At the time, I was the Moscow bureau chief for Business Week. Berezovsky’s people had promised me a good story on how their man was setting up an opposition campaign against Putin, and they encouraged me first to talk to Litvinenko—or “Sasha,” as they all called him—as part of the tale.

I knew little about Litvinenko except that he had defected from the FSB and was now, like the oligarch, making monstrous accusations against Putin and the Russian security services. I was sufficiently intrigued to agree to lunch, and we walked from our rendezvous spot in Mayfair—just outside of Berezovsky’s offices on Down Street—to a  restaurant, Digress, off of Regent Street. Litvinenko, barely eating, talked on and on; I had trouble keeping up with him. By the time I called a halt to the interview, I felt saturated with “facts” that I could barely digest—and he looked revved for action. Clearly this was a man on a mission.

I have now read through the interview notes a number of times. What comes across, as much as anything, is Litvinenko’s dependency, in almost every way, on Berezovsky. That is of itself interesting, since Scotland Yard is undoubtedly probing the tie between Litvinenko and the oligarch. Traces of polonium 210 were reportedly found at Berezovsky’s offices in a sweep conducted after Litvinenko’s death. And Litvinenko apparently visited Berezovsky within hours of a lunch, on Nov. 1, at which the former secret-service man supposedly ingested the poison.