Overlong and grim to the point where some scenes are virtually unwatchable, this Australian docu-drama was inspired by a gruesome series of serial killings in a suburb of Adelaide where dismembered, rotting bodies were found stashed in barrels inside a closed bank in the late 1990s.

The story is told from the point of view of a youngster (Lucas Pittaway), who’s drawn into this horror as an accomplice by his mother’s boyfriend John Bunting (Daniel Henshall), an anti-pedophile vigilante who turns out to be the worst serial murderer in Australia’s history.

Employing a cast with accents so thick that subtitles would help, “Snowtown Murders’’ director Justin Kurzel seems to be dubiously arguing that Bunting’s crimes were the inevitable byproduct of poverty, addiction, domestic violence and sexual abuse.