For years, it was believed that Joseph Naso, the 'Alphabet Killer', only had four victims. But while behind bars, Naso began confiding in a fellow death row inmate, William Noguera. Naso would frequently brag about his crimes, including ones of which he hadn't been convicted. Little did he know, William was determined to bring justice to the victims and take down Naso in the process.

Retired FBI Task Force Investigator and Cold Case Detective Ken Mains discusses how he formed an unlikely team with William, and how they worked to solve Naso's cold case murders, as detailed in the new docuseries, Death Row Confidential: Secrets of a Serial Killer.

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