I think it should be in the running for one of the top ten stories of the past decade. Raised lots of questions about the practical science behind "the first incident of nuclear terrorism in history". Yet, though I vaguely remember the news accounts at the time, not THAT big of a deal was made of it. At least not publically in the USA. It happened in England, where it probably caused a greater hue and cry.
One would think, behind the scenes, that some consternation arose due to the much greater difficulty of detecting Polonium, with it's "alpha" radiation, as opposed to, for example, Uranium with it's "gamma" radiation. It was achieved, only after the fact, once authorities knew what to look for, since Polonium leaves a persistent trail.
Following that detection trail from restaurants, to offices, and to hotel rooms (England and Germany), with specific planes and seat assignments uncovered, and realizing the difficulty of detection concurrent with actual polonium presence, was creepy.
Though the intransigence of the Russians toward foreign investigators was, perhaps, understandable, the evidence suggests a state sponsored assassination. Also creepy.