Mr. Litvinenko spent his time in London writing anti-Putin diatribes, giving interviews to novelists and filmmakers interested in post-Soviet Russia and trying, for the most part unsuccessfully, to drum up work as a security consultant. In their interviews with Mr. Cowell, Mr. Litvinenko’s acquaintances, friends and even family frequently said he talked too much, was obsessed with Vladimir V. Putin in an unhealthy way and came across at times as crazy. His own father, referring to Mr. Litvinenko’s childlike view of the world, said, “He was a bit like Forrest Gump.”  One of the enduring mysteries of Mr. Litvinenko’s murder is why anyone would go to the trouble of killing such a small-time player. Mr. Cowell lays out the great variety of theories: Mr. Litvinenko was gathering information on shady dealings in the Russian oil business and upset powerful people; Mr. Litvinenko’s connection to Mr. Berezovsky made him a stand-in target for him; Mr. Litvinenko’s former colleagues in the F.S.B. were furious over his public denunciations and, assuming he had been debriefed by British intelligence, considered him a traitor who deserved to die.  Probably the most spectacular of the theories is that Mr. Litvinenko was killed for revealing in an interview that he had been told that the Italian prime minister at the time, Romano Prodi, was a K.G.B. agent.  We may never know precisely why Mr. Litvinenko was murdered, but the British police were able to determine, at least to their satisfaction, how he was murdered. One of polonium’s attributes is that the smallest traces of it will “spill, tumble, rise on air currents, attach to surfaces and solidify.”  Mr. Cowell follows the British investigation as the police chase the traces of the isotope around London, reconstructing the chronology of events on the day of Mr. Litvinenko’s murder. For everyone who’s tired of the endless forensic investigations that take up so many hours on television and so many pages in crime novels, this nuclear street work is engrossing in a whole new way.  Ultimately, the trail led to a Russian businessman and former K.G.B. bodyguard named Andrei Lugovoi. Russia refused to extradite him, and since there has never been a court case, much of the evidence against Mr. Lugovoi has remained sealed. Mr. Lugovoi asserts that he himself was a victim of the polonium attack, which is why he left traces of the element everywhere he went.  As the multiple subtitles in Mr. Cowell’s book suggest, he believes that the Litvinenko murder has far-reaching significance. He argues that the West has become embroiled in a new cold war with Russia, and that Mr. Litvinenko’s poisoning, whether authorized at the very top or not, was the act of an angry, newly ascendant Russia. He also believes that the murder was the world’s first act of nuclear terrorism, and that the use of polonium or similar elements in a slightly modified manner could be much more effective for terrorists than a dirty bomb.  Mr. Cowell’s warnings about this may or may not prove to be prophetic, but it’s hard to see Mr. Litvinenko’s assassination itself as an act of terrorism, rather than just as a brutal and particularly twisted murder. Perhaps Mr. Litvinenko’s father captured it best when he described what happened to his son as a “tiny” nuclear attack.  As for Mr. Litvinenko’s suspected killer, Andrei Lugovoi went on the offensive, publicly attacking the British and their case against him. His nationalist, anti-Western stance was so popular at home that he was elected to the Duma, the Russian Parliament’s lower house.  In a world where a decent, naïve and ultimately harmless man like Alexander Litvinenko is poisoned by radioactive tea, it’s hardly a surprising conclusion to this story.  Joseph Weisberg worked in the Directorate of Operations of the Central Intelligence Agency in the early 1990s and is the author, most recently, of “An Ordinary Spy.”  A version of this review appears in print on , on Page E2 of the New York edition with the headline: Bizarre Death of the Man Who Talked Too Much. Today's Paper|Subscribe
Alan S. Cowell, a New York Times correspondent, gives an absorbing account of a murder and tries to determine if it is the harbinger of a new kind of terrorism.