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.

Serial killers often live fairly ordinary lives with normal employment, enabling them to blend in with colleagues. Their legitimate jobs also offer them one more key perk: an opportunity to help carry out or conceal their crimes, according to experts.

Dressing in disguise is a time-honored Halloween tradition where self-expression and secrecy often meet. But costumes can also serve a much more sinister purpose. Learn about murderers who literally dressed to kill.