Season 4 - Episode Guide

: With a total of 49 confirmed murders, Gary Ridgway, otherwise known as the Green River Killer, is one of the most prolific serial killers in American history.

A mass suicide by members of a religious cult called Heaven's Gate, led by Marshall Applewhite, is the focus.

Ted Kaczynski's deadly bombs and his survivalist lifestyle are the focus.

NFL player Aaron Hernandez and the murders he committed are the focus. Also: a look at his suicide in prison.

Pregnant 18-year-old Melissa Drexler gives birth to her son in a bathroom stall during her prom; the miraculous moment turns into murder when the teen suffocates the child, wrapping him in a plastic bag and discarding her baby in the trash.

Notorious gangster, Whitey Bulger, was one of the most prominent figures in Boston's organized crime scene. From 1975 to 1990, Bulger also served as an informant to the FBI and tipped off police of other crime families while simultaneously building his own crime network. Bulger spent 12 years on the FBI Ten Most Wanted Fugitives list for charges that included racketeering, extortion, conspiracy and 11 murders. Bulger was the subject of the 2015 film Black Mass, starring Johnny Depp as the crime boss himself.