Opens: Friday, Oct. 31 (New York); Friday, Nov. 7 (Los Angeles) (Oscilloscope Laboratories)

For many storytellers and their audiences, there's no denying a certain fascination with the murderous impulse. Whether the tales are fact-based or fictional, the workings of the twisted psyche enthrall.

But when Kurt Kuenne set out to make a documentary tribute to a murdered friend, he had no intention of going there. His interest was young doctor Andrew Bagby, not the ex-girlfriend who, overwhelming evidence indicates, shot him to death in a Pennsylvania park before returning to her native Canada and giving birth to his son.

Aiming to provide a memento for Bagby's friends and family, Kuenne embarked on a cross-country road trip to interview the many people who knew and loved his lifelong friend. By connecting with them, he clearly was trying to sort out his sorrow -- his voiceover narration is self-questioning as well as informative. Fueled by equal parts love and rage, "Dear Zachary: A Letter to a Son About His Father" is an anguished cry of a film.

It's also a deftly orchestrated portrait of Bagby and his parents, who moved from California to Newfoundland to pursue custody of their grandchild and monitor extradition hearings for accused killer Shirley Turner. Intercutting footage of Bagby and his father, Dave, Kuenne finds poignant rhyming gestures. Zachary, born eight months after Bagby's November 2001 murder at 28, bears an eerie resemblance to his dad. To be near their grandson, the Bagbys had to endure lengthy dealings with the manipulative Turner -- engaging in a "dance with the devil," as Dave Bagby titled his 2007 book.

As one unspeakable event leads to another, Kuenne's film turns into a chilling crime thriller and a stinging indictment of a Canadian justice system that repeatedly extended an absurd degree of deference to a woman charged with murder. Without becoming a screed for victims' rights, the riveting film shows how in the face of terrible events a grieving parent is galvanized into activism.

Production: An Oscilloscope Laboratories presentation in association with MSNBC Films.
Writer-director-producer-director of photography-composer-editor: Kurt Kuenne.
No MPAA rating, 93 minutes.