Filmmaker Kurt Kuenne began this home-movie scrapbook as a memorial tribute to his best friend Andrew Bagby, most likely murdered by an unstable ex-girlfriend. But Kuenne had to shift gears when the suspect fled to her native Canada and announced her pregnancy with Bagby’s son. Little Zachary was born with his grandparents battling the Canadian judiciary to bring his mother to justice and Kuenne just as zealously gathering material for a portrait of the father he’d never know. Then something even more horrible happened, and Dear Zachary had to change course again. The result is understandably jittery, and urgently provocative. With material so raw, the movie’s lack of craftsmanship sometimes works to its own advantage. It’s about as personal as a documentary can get.