In "The Devil in the White City," Erik Larson references Dr. Hervey Cleckley's influential work, "The Mask of Sanity," which presents the idea of the psychopath as a highly sophisticated mimic of genuine human behavior. Cleckley describes these individuals as having the ability to replicate human emotions and personality traits so convincingly that they appear indistinguishable from normal people during clinical assessments.

This extraordinary ability of Cleckley psychopaths to deceive others highlights the challenges in identifying such disorders, as no obvious signs can be categorized scientifically or objectively. As a result, these individuals can navigate society unnoticed, displaying behaviors that often leave a lasting impact on those around them.