S4 E1 • Hog Trail Murders

In central Florida, the bodies of four men are found in a wooden area known as The Hog Trails. Police realize they are chasing a serial killer, but the investigation is hampered by the fact that they are unable to identify any of the victims. Finally a fifth body yields a name, and soon puts authorities on the trail of nurse Daniel Conahan.

S4 E2 • Yosemite Park Murders

What begins as a search and rescue becomes a chilling case of murder. An attractive motel handyman uses forensic science to mislead and manipulate investigators in the murders of a mother, daughter and two young women in Yosemite National Park.

S4 E3 • House Hermit

An elderly couple is found dead in the trunk of their car at their home in Toronto. The investigation eventually leads to the couple's vacation home an hour north of the city. Police soon learn of the "House Hermit" a mysterious intruder breaking into area cottages and camping in them. He becomes the prime suspect, but though police finally identify him they cannot find him anywhere.

S4 E4 • Sniper

For 23 days in October, 2002 a sniper terrorizes the Washington DC area, shooting thirteen people and killing then. Authorities struggle to find a clue until they discover a single fingerprint, which leads to not one, but two killers, including a seventeen year old boy.