One of the recurring themes at this year's Sundance Film Festival is that of redemption. In Amy (daughter of Robert) Redford's The Guitar, a terminally ill woman acts out a pre-adolescent temper tantrum in order to resolve adolescent issues before she dies. In The Visitor, a crotchety, frustrated professor is given a new lease of life by an unexpected lodger. And in the opening film In Bruges, a hitman (played by Colin Farrell) becomes an unlikely poster boy for forgiveness after accidentally shooting a child on his first mission. Even The Great Buck Howard, a lovely comedy about an ageing hypnotist played by John Malkovich, suggests that even the seemingly unlovable have their softer sides.

But in the 30th anniversary of his most awful hour, the question remains: can the world ever really put its arms around Roman Polanski? After all, despite his talent, his indubitable charm and his famous good humour, the crime that this emigrant director was so famously accused of, and successfully prosecuted for, was not simply an error of judgement, like a DUI or tax evasion. In his mid-40s, Polanski had sex with a 13-year-old girl at his friend Jack Nicholson's house. Fearing, with good reason, a stiff jail sentence, he fled to Paris in 1978 and never returned. Now, in his 70s, he lives a respectable life in Paris, with his wife of 18 years and two children.

Polanski's flight from justice is the basis of Roman Polanski: Wanted and Desired, an engrossing and enjoyable but not necessarily thorough documentary on the Polish-born director that raises more questions than it actually answers. To be blunt, it functions better as a collage than a feature film, assembling some wonderful archival material, most notably involving Polanski's sad, stunning wife Sharon Tate – murdered in 1969 by hippie misfits. These clips beautifully evoke the wanton atmosphere of the 1970s, giving a lovely platform to a cop who wonders aloud, and with a big grin, whether the beatific Polanski ever really knew what it meant to be under arrest in America at all.

This stuff is gripping and involving, but after a while Marina Zenovich's film starts sending its sparks in very different directions. Polanski's 'genius' is assumed, which may be maddening for those who aren't too familiar with his better works and his heyday, and far too much time is spent on the details of Polanski's trial, involving a showbiz-courting judge whose star-struck ways finally got the better of him. And most annoyingly of all, the girl who charged Polanski in the first place is interviewed and never really challenged. Why has she forgiven him? Why does she go so easy on her mother, who so clearly put her in harm's way? And what are her motives for going public now?

It's a measure of this 100-minute film's success that viewers are left wanting more, but it still makes for uncomfortable viewing, particularly given Polanski's almost cheerful acceptance of the count of unlawful sex with a minor that he plea-bargained for. And ultimately, this is the film's only true failing. Though it is by no means a film-maker's prerogative to moralise, it is certainly the film-maker's place to situate themself in the ballpark. Zenovich's film doesn't come close, and for many people who neither know nor care about Polanski's groovy Hollywood reputation, this dark tale may seem unsavoury indeed.

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