When does a documentary end and fiction begin? The question pops up frequently enough to suggest that there's no easy answer, especially when a clearly autobiographical element is included.

This week's example: the single-named writer-actor-director Maïwenn's "Polisse," which focuses on a photographer who is embedded in France's Child Protection Unit. That part is fiction, yet the script is based on Maïwenn's real experiences with the CPU.

She observed as they tracked down and punished child molesters, rapists, parents and teachers who justify their frequently outrageous behavior with declarations like, "We had a relationship that was like love." She also runs into a few children who apparently exaggerate or lie to attract attention and affection.

Still, there's never much doubt that serious crimes have been committed against at least some of these kids. Their answers to police interrogators are often astonishingly frank; so are the responses of adults.

"He was nice to me," says one almost-grateful victim of abuse, echoing the moral dilemma at the center of John Patrick Shanley's troubling film and play, "Doubt."

All of this is filmed in a sprawling, jumpy style that suggests "reality TV" or the kind of ensemble piece that the late Robert Altman perfected. Maïwenn encouraged her actors to forget the cameras and relax into a revealing improvisatory technique.

Some moments suggest that the actors weren't conscious that they were being recorded at all (a child picks his nose and tastes the result), while others seem soapy or melodramatic (a couple indulge in shouting at each other).

Other touches seem accidentally comical. An admitted bigamist turns out to have a very limited sexual vocabulary. A game of charades somehow links Jean-Luc Godard's "Contempt" with Gerald Thomas' "Carry on Camping."

The shock ending, which may seem to come out of nowhere, will offend many. It also will stimulate discussion. Whatever you think of it, you won't be neutral.

John Hartl: johnhartl@yahoo.com