The story of Alexander Litvinenko is fascinating.

A high-ranking officer in the Russian spy service, known as the FSB, he fled the country in 2000 after accusing the organization of widespread corruption. He said publicly that his superiors had ordered him to kill the Russian oligarch Boris Berezovsky and that the FSB was responsible for the bombing of Moscow apartment buildings in 1998 — not Chechen terrorists, as had widely been reported.

Litvinenko and his wife and young son settled in London, where he had sought and received political asylum under the aegis of Mr. Berezovsky, who had also found refuge there as an outspoken critic of the Russian government and its president, Vladimir Putin.

The former spy became an international sensation in November 2006 when he fell ill with a mysterious ailment, eventually found to be radiation poisoning, and died weeks later in a London hospital. Suspicion initially focused on a London sushi restaurant, where he had dined with an Italian associate, but later settled on two former FSB agents, with whom Litvinenko met afterward for tea at the Millennium Hotel.

Britain’s investigation ground to a halt last summer after Russia declined to extradite one of the ex-FSB officers, Andrei Lugovoi. Diplomatic maneuvering ensued, and Russian-British relations remain tense today.

A more exciting premise for a documentary could scarcely be found. It is all the more disappointing, then, to report that Andrei Nekrasov’s “Poisoned by Polonium,” which makes its premiere Friday at Quad Cinemas, is utterly unexciting.

Screened at Cannes as “Rebellion: The Litvinenko Case,” the film is muddled where it should be straightforward, and Nekrasov-centered when the focus should be on Litvinenko. As the movie shuffles through post-Soviet history and the Chechen wars, Mr. Nekrasov, recognized in Russia as a playwright, theater director, and filmmaker, provides an English voiceover for diversions to his own ransacked apartment, clips of himself on Russian television (“my documentary was one of the last independent on Chechnya shown on NTV”), his early search for the ex-spy (“I mobilized scores of my acquaintances to find Litvinenko”), and, most egregiously, chats with a French intellectual and a German (the director speaks German and French, too!).

Scenes of Litvinenko, whom Mr. Nekrasov managed to interview before his poisoning, are frustratingly brief, and as the subject speaks, the camera wanders off in all directions. Still, these scenes provide the highlights of the film. Mr. Lugovoi, now a member of the Duma, Russia’s parliament, makes an appearance, offering Mr. Nekrasov tea. The filmmaker, who appears to take it as a given that the FSB officer-turned-parliamentarian poisoned Litvinenko’s tea with polonium-210, swiftly declines. Meanwhile, Mr. Putin and his FSB apparatus are portrayed exclusively as villains, and sinister music accompanies every shot of the outgoing president.

Left unexplored in the film is Litvinenko’s relationship with Mr. Berezovsky, who is shown in a short interview with Mr. Nekrasov describing the “Russian mentality” as “deeply slavish.” Was Mr. Berezovsky — once the chief of a vast automobile, airline, oil, and press and broadcast empire — Litvinenko’s patron, friend, employer? What was the ex-spy doing for a living at the time of his death, and why did he meet with the Italian lawyer Mario Scaramella and later with Mr. Lugovoi and his associate, Dmitry Kovtun, on that fateful day?

There is a fascinating documentary to be made on the Litvinenko mystery. Mr. Nekrasov, however, has squandered his opportunity with “Poisoned by Polonium.”

mmercer@nysun.com

For more on the Litvinenko case, please see Edward Jay Epstein’s “The Specter That Haunts the Death of Litvinenko“.