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.

In 2003, Steven Mack, a homicide detective with the Huntington Beach Police Department, took a leading role in retrying a twice-overturned murder case against Rodney Alcala. His efforts led to the uncovering of a prolific serial killer.

The Baton Rouge serial killer murdered eight women in Louisiana between 1994 and 2004, around the same time serial killer Derrick Todd Lee was also active in the area.

Susan Jonusas talks to us about her book 'Hell's Half-Acre' about a 'family' of four known as the 'Benders,' who were accused of murdering 11 people in Kansas but fled before they were prosecuted.

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 the 1990s and early 2000s, more than 30 women were targeted by serial killers, including Derrick Todd Lee, in the Baton Rouge area.

Dr. Marissa Harrison, an evolutionary psychologist and author, speaks to us about her research on female serial killers and how she was impacted by victims' stories.

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.

From German nurse Niels Högel to U.K. doctor Harold Shipman to American nurse Charles Cullen, some serial killers target their patients.

Robyn Maharaj, co-author of 'Grilling Dahmer' with Milwaukee detective Patrick Kennedy, tells us about the late detective's experience with the serial killer.