When amateur historian John Maloof purchased a box of negatives at a Chicago storage-unit auction in 2007, he became obsessed with tracking down the photographer behind the thousands of stunning shots. Enter a reclusive figure: the late Vivian Maier, a nanny who'd spent decades taking engrossing, slice-of-life street photos on her Rolleiflex, only to hide them from the world. In his documentary Finding Vivian Maier, Maloof and codirector Charlie Siskel interview employers and others in her life to uncover a woman of bewildering paradoxes. Some remembered her as a joyous adventurer, some as a woman harboring a mysterious trauma. None knew her as a photographer whose work would one day be compared to that of Robert Frank, Lisette Model, and Helen Levitt. The Oscar-winning Searching for Sugar Man, a similar fanboy detective story, found its protagonist, but Maloof and Siskel are ultimately left with the specter of a woman who lived two lives—one troubled and hidden, the other behind a camera. Out March 28.