What is evil—and how do we measure it? Is it more evil to abduct and torture a stranger for days before ultimately letting them go, or to fatally shoot a spouse in a fit of jealous rage? We speak to clinical psychologist Dr. Gary Bucato, co-author of the new book, 'The New Evil,' about how he determined what acts are more evil than others and why serial killers aren't all categorized the same way.

'Dirty John,' real name: John Meehan, was a criminal, con artist and master manipulator known for preying upon women in various states who he considered easy targets. A&E True Crime dives into the backstory of the infamous lothario known as Dirty John.

To find out how one might escape a captor, A&E True Crime spoke with Lt. Chris Zimmerman, commander of the New York Police Department's Hostage-Negotiation Team.

Read an excerpt from the book 'Life After Darkness: Finding Healing and Happiness After the Cleveland Kidnappings,' by Michelle Knight, now known as Lily Rose Lee.