As any fan of Raymond Chandler - or, heck, even Columbo - will tell you, sometimes even the most self-interested of investigators can stumble on the truth. Drawling gadfly Nick Broomfield probably wouldn't be your first choice to make a human-rights epic, but in sticking to this desperately sad story of Aileen Wuornos, a tragic, damaged woman, he's ended up on the side of the angels.

This is not the laconic, distanced filmmaker of Kurt And Courtney. Broomfield here is closer to the rampaging Michael Moore, raging against the politically expeditious execution of "hitchhiking hooker" killer Wuornos and the unholy circus of self-interest and sanctimony swirling around her.

A choppy doc, it nevertheless presents enough persuasive footage of an unstable Wuornos to give real weight to Broomfield's anti-death-penalty message. That the director is so close to his subject - he first covered her story for a 1992 documentary, Aileen Wuornos: The Selling Of A Serial Killer - only adds to the power.

Inevitably, we also get endless wavering shots of motorways from car windows, the patented faux-naïf Brit-abroad act and a front-row view of all events starring Broomfield himself. There's no shaking the suspicion that Aileen is partly a self-serving vanity project, Broomfield again rippling controversy to raise his own profile. No matter. This compelling, thought-prodding doc allows the bigger picture - cogent, angry, even passionate - to shine through.