The nonfiction-film genre has grown fast, cheap, and out of control lately with the democratization of digital video cameras and iMovie. Much agitprop on politics and the environment is out there masquerading as documentary work. No longer do filmmakers feel the necessity to spend years tracking the development of a subject. So it’s extraordinary to finally see a film worthy of comparison to Errol Morris’s seminal The Thin Blue Line arriving two decades later. A lifetime in the making, Dear Zachary: A Letter to a Son About His Father investigates the murder of doctor Andrew Bagby, whom director Kurt Kuenne had known and filmed in home movies since they were childhood friends. Bagby’s ex-girlfriend, Shirley Turner, emerged as the prime suspect, and escaped to Canada while pregnant with their unborn son. Upon learning of this, Kuenne set out to interview everyone Bagby ever knew so that baby Zachary would one day get to know his dad. Meanwhile, Bagby’s parents relocated from California to Newfoundland to fight for custody of their grandson when it seemed there was no end to Turner’s extradition process. Kuenne lovingly assembles home-movie footage and new interviews, while deftly borrowing a narrative trick from fiction—the plot twist—to create a true-crime story so gripping, devastating, and ultimately unforgettable that it easily trumps any thriller Hollywood has to offer this year.