Near the start of Alex Gibney’s documentary “Crazy, Not Insane,” his subject asks the kind of essential question that feels so unanswerable that it is brought up not nearly as often as it should be. Thinking about the nature of evil and recalling her childhood interest in the Nuremberg Trials, she asks very plainly, “How come I don’t kill?” Everyone gets angry. But not everyone commits bloody murder. Barring answers of a spiritual nature, squaring that circle will necessarily involve spending time with some very unpleasant people, which is exactly what the woman who asked the question spent a career doing.

READ MORE: The Best Documentaries Of The Decade [the 2010s]

A forensic psychiatrist with the chipper, eager demeanor of somebody who spends a good part of her day chuckling about the delightful strangeness of the world, Dorothy Otnow Lewis started her career working with juvenile delinquents. She discovered that many of the homicidally-inclined ones had some combination of mental dysfunction and childhood abuse. Believing in her core that “murderers are made, not born,” she dove deeper into the subject. This led her to interview over 20 serial killers to see if she would find similar backgrounds. She did.

READ MORE: 2020 Fall Film Preview: 40 Most Anticipated Films To Watch

As far as that goes, Lewis is a solid but none-too-surprising subject for Gibney to base an entire movie around. While the linkage between childhood trauma and later antisocial or criminal behavior has been well-known for some time, the belief that crimes are committed only by people in full command of their senses remains fairly widespread. To illustrate what Lewis describes as the American justice system’s turn from rehabilitation to punishment, Gibney drops in clips of Hillary Clinton and Joe Biden’s scaremongering speeches about villainous young criminals who deserved nothing but a jail cell. If the movie had stuck with digging into the psyches of killers who, had they been raised by different parents or had no brain abnormalities scrambling their decision-making capabilities, might have never hurt anyone, it would have come up with a more convincing avenue for answering the question posed by Lewis at the start.

READ MORE: The 20 Best Documentaries Of 2018

But it does not. Somewhat early on, Lewis starts delving into multiple personality disorder. When she started delving into the subject, it had fallen out of favor with the mental health community. When she talks about her examination of a serial killer like Arthur Shawcross, it is not hard to see why. On trial for several gruesome, quasi-cannibalistic murders, Shawcross appears in his taped interview with Lewis to speak in different voices as different personalities inhabiting the same body. But the voices are inconsistent, and as a forensic psychiatrist for the prosecution argues, Lewis’ delivery in the interview could be seen by some as coaching and suggestive.

READ MORE: The Best Films Of 2020… So Far

Lewis’ proposal, that victims of serious trauma inflicted on them at a young age disassociate from the abuse being inflicted on them as a survival technique, makes absolute sense. But her argument, or at least the version of it that Gibney includes here, that such victims turn their disassociation into one or more personas (which she calls “alters”) that function as invented protectors is somewhat harder to swallow. When she describes interviewing Ted Bundy, looking for evidence of familial trauma despite his insistence that his childhood was unmarred by abuse, it is difficult to think of anything but a hammer looking for a nail.

Perhaps the factor that keeps “Crazy, Not Insane” from cohering into a gripping narrative, despite its charming absent-minded professor of a subject, is its inability to come to grips with the question at its core. Gibney has recently released a lot of work, with some of the better examples like “Totally Under Control” and “Agents of Chaos” functioning as well as they do because of how hard he drives for the net. “Crazy, Not Insane,” like the very non-linear Lewis, meanders through several tangents (the death penalty, parsing the nonsensical definition of legal insanity) without ever quite arriving anywhere. [C+]

“Crazy, Not Insane,” streams on November 18 on HBOMax.