In Werner Herzog’s new documentary, “Into the Abyss,” sorrow spreads like an oil slick on water. The movie finds, in a relatively banal, thoroughly senseless American story of crime and punishment, enough darkness to make you wonder about the title. Is death, which unites murderers with their victims and executioners, and ultimately with everyone else, the abyss that Mr. Herzog wants us to contemplate? Or is he directing our attention toward a black hole that sits in the middle of life? The paradox of this film is that it is both unremittingly bleak and rigorously humane. Mr. Herzog, interviewing killers, survivors, witnesses and officials in law enforcement and corrections, is polite even when asking uncomfortable questions, and the seriousness of his intentions allows humor and absurdity to bubble up amid all the pain. He never appears on camera, but his unmistakable voice — dry, precise, carrying the accent of his native Bavaria — ties together this tapestry of conflicting testimony, inchoate emotion and unredeemed ugliness. In its alternation of talking-head interviews and archival video clips, “Into the Abyss” superficially resembles the kind of titillating, moralizing true-crime shockumentary that is a staple of off-hours cable television. But the grim ordinariness of the narrative makes its Dostoyevskian dimensions all the more arresting. In October 2001, in Conroe, Tex., Sandra Stotler, her son Adam and his friend Jeremy Richardson were murdered, apparently because the killers wanted the red Camaro in Ms. Stotler’s garage. About a week later, after a shootout in a shopping center parking lot, two young men were arrested in the case. One, Jason Burkett, received a life sentence. The other, Michael Perry, was sentenced to death. Mr. Perry was interviewed for “Into the Abyss” through penitentiary plexiglass eight days before the scheduled date of his execution, in the summer of 2010. He has a lively, ingratiating manner, though his protestations of innocence and his expressions of religious faith may not seem entirely convincing. But Mr. Herzog is not interested in vindicating any particular point of view or version of events. Nor, despite his clearly stated moral opposition to capital punishment, is he advocating a political position. He is instead — as he so often has, in fictional features and documentaries alike — probing the contradictions of the human heart, in which nobility and savagery are so entwined as to be almost indistinguishable. After a preliminary, and unexpectedly revealing, chat with a death row chaplain, Mr. Herzog plunges into what you might call the philosophical forensics of the Conroe murders. He listens patiently as a courteous sheriff’s deputy reconstructs the investigation, and allows himself to wonder why the crime took place. Conversations with Mr. Perry and Mr. Burkett don’t yield a satisfying answer, but as the film pursues the facts of the event it paints a vivid and disturbing picture of the broken society that made their crimes possible. This is not to say that “Into the Abyss” offers sociological theories or right-thinking pieties about the causes of violence. There are references to drugs and poverty, and intimations of serious family dysfunction, but there is also ample evidence of love, loyalty and righteousness. And if Mr. Herzog is never overtly judgmental, he is not aloof or neutral, either. What makes the film bearable — what keeps the viewer just at the near edge of despair — is the ethical passion that drives his inquiry and his compassionate curiosity about how people make sense of their own actions and motivations. Mr. Herzog is an excellent listener, a quality that distinguishes his recent documentaries, notably “Grizzly Man,” “Encounters at the End of the World” and “Cave of Forgotten Dreams.” All of those, come to think of it, could have been called “Into the Abyss” — the title would also suit “Aguirre, the Wrath of God” and just about anything else starring Klaus Kinski — and this film is linked to its predecessors by a fascination with human behavior in extremis. What is most disconcerting for an American viewer is how close to home the extremity is, as if the heart of darkness lurked among your friends and neighbors. And this is true even as you recognize their decency and empathize with their anguish. It is impossible not to be moved by the testimony of Lisa Stotler-Balloun, whose mother and brother were so cruelly taken from her. An interview with Mr. Burkett’s father, who is serving a long prison sentence, is also heartbreaking: a chronicle of waste and failure delivered with unflinching, plain-spoken honesty. Finally, what rescues “Into the Abyss” from its title is the stubborn individuality of the people it discovers, none of them entirely innocent or utterly evil, all of them vivid and memorable. They cling to life and look for meaning in its darkest episodes with a tenacity that drives home the terrible price of killing, whether it is a result of criminal impulse or state policy.