Her eyes locked onto him as soon as she entered the courtroom: Otto Adolf Eichmann, a Nazi butcher in the flesh, caged in a glass box.

It was 1961, and Hannah Arendt had come to Jerusalem to cover Eichmann’s sensational trial for The New Yorker. The case would put the world’s spotlight on the details of the Holocaust.

Eichmann had been responsible for transporting Jews to the concentration camps, and was only second-in-command to Holocaust architect Reinhard Heydrich.

Yet the more that prosecutors framed Eichmann as an evil mastermind, the more perplexed Arendt became... The man across from her did not seem like not a monster, but a mediocrity.

She saw the receding hair, bad teeth, and nervous tic of a man who did not appear to be cruel at heart, who had no history of anti-Semitic activity, and whom six psychologists had judged neither morally nor legally insane.

It was a jarring sight for Arendt who, as a German Jew herself, had once been imprisoned by the Nazis before seeking refuge in France and finally the United States.

Expecting a villain with no conscience, she instead detected an insecure man whose hunger for status and promotion led him to obey orders, whatever they were.

This raised serious questions about human nature: Were the engineers of the Holocaust inherently evil? Or were they just normal people whose lack of a moral compass allowed them to do horrible things?

As for Eichmann, were his actions technically lawful because they occurred within a legal framework? Could they be considered justified by the prevailing moral code of the time?

Arendt explores these complex issues in her controversial book Eichmann in Jerusalem. It’s an extraordinary look at the everyday face of evil. Here’s what she found...