Five of the Chicago serial killer's 33 victims from the 1970s remain unidentified, but the Cook County Sheriff's office is continuing the work to ID them.

Read about the life and death of Tim McCoy, serial killer John Wayne Gacy's first known victim. Gacy murdered at least 33 boys and men between 1972 and 1978

During his 1980 trial, evidence against the serial killer was so strong that his guilt was not in question. Instead, the case hinged on whether he'd been legally insane when he killed.

Margaret Press, co-founder of DNA Doe Project, spoke with A&E True Crime about how investigative genetic genealogy helped identify Francis Wayne Alexander as Victim No. 5 of serial killer John Wayne Gacy.

According to testimony from friends and family, victims of the "Killer Clown" shared some surprising common connections and tragedies in their lives.

Read about the death of the businessman and children's entertainer, who liked to dress as 'Pogo the Clown' and was convicted in March 1980 of murdering 33 boys and young men, making him the worst serial killer in American history at the time.

Investigative historian Peter Vronsky explains how Edmund Kemper, Ted Bundy, Jeffrey Dahmer and others reached celebrity status during the 'Golden Age' of American serial killing.

The serial killer seemed to be a well-adjusted adult. But his crimes included binding, torturing, raping and ultimately murdering 33 male victims, some as young as 15 years old.

From 'Kayak Killer' Angelika Graswald to cult leader Charles Manson, A&E True Crime looks at infamous criminals who profited in some way from their misdeeds, showing that sometimes crime does indeed pay.

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.