'Crazy, Not Insane' explores the life's work of a serial killer researcher

As a sheltered Jewish girl in 1940s New York, Dorothy Otnow Lewis listened to the news of the Nuremberg Trials broadcast on her parents' radio. She heard the depressing revelations of the psychopathology of what had made the Nazis so evil.

When she left home in the '60s to become a psychiatrist, her morbid childhood fascination with the inner workings of evil men led her to specialise in the investigation of what made serial killers tick.

Over a decades-long career in which she showed a stubborn determination to her cause of trying to understand people whose evils made them incomprehensible to many, Lewis came to be one of the most vocal advocates for the idea of dissociative identity disorder, the more clinically correct term for what in popular consciousness is called multiple personality disorder. She used this as a tool to understand the motivations of these very damaged men.

Alex Gibney's documentary Crazy, Not Insane offers a fascinating exploration of Lewis's personal struggle to gain acceptance for her theories. It draws on many hours of deeply uncomfortable video and audio interviews conducted over decades by Lewis with some of the 20th century's most notorious serial killers.

Lewis's theory that murderers are made and not born was popular with defence attorneys looking to save their clients from the electric chair but it was deeply unpopular with those who wanted to see killers, like Arthur Shawcross and Ted Bundy, burn in hell for their sins.

Her many public appearances in televised trials and on talk shows made her the visible face of a theory that many saw as an attempt to excuse the actions of cold, calculating psychopaths and relieve them of responsibility for their crimes.

But Lewis's dedication to building a theory based on a persuasive set of recurring patterns offers a strong basis for admitting that external factors do play a role in the creation of these monsters and, to some extent, shows the reasons for their actions. They often had traumatic childhood abuse, which led them to strictly compartmentalise their lives - which in turn allowed them to act in unspeakable ways while still believing that they were not monsters.

Gibney allows his subject and the archive of her research to take the floor and doesn't intervene with any real analysis of broader social or historical circumstances as he has in his other films.

Thanks to her intelligent presence Lewis makes a compelling argument for the significance of her life's work and its importance in allowing us to think in new, more philosophically productive ways about evil, justice and retribution. You may not agree with her but you'll find it hard not to at least listen and think about what she has to say. 

• 'Crazy, Not Insane' is available on Showmax.