A former nurse turned FBI profiler interviewed dozens of killers. She explains what the most dangerous ones have in common.

Candice DeLong speaks onstage during A True Crime Experience Live at Gotham Hall in 2023. Ilya S. Savenok/Getty Images for Wondery Candice DeLong shifted from psychiatric nursing to a 20-year career in the FBI profiling killers. DeLong's career insights show that lack of guilt defines the most dangerous serial killers. DeLong found that success after a first murder often encourages serial killers to continue killing. Candice DeLong didn't plan to spend her career interviewing killers. She…