Harold Henthorn calls 911 to report that his wife Toni has been gravely injured after falling off of a cliff on a remote trail. National Park Service Special Agent Beth Shott uncovers suspicious details and inconsistencies in Harold’s story.

As Special Agent Shott investigates the suspicious death of Harold’s wife Toni, anonymous letters and phone calls lead authorities to reopen an investigation into the death of Harold’s first wife 17 years earlier.

As the investigation into the suspicious death of Toni continues, Special Agent Shott learns something startling about Harold’s unusual relationship with his sister-in-law. Shott is joined by FBI agent Jonny Grusing who specializes in serial killers.

A search of the Henthorn home leads investigators to expose one of Harold’s biggest secrets. Shott and Grusing, her FBI partner, are confident that Harold murdered Toni, but they must assemble an airtight case with every scrap of evidence they can find.

Yosemite: a hand is found, a serial killer confesses. But he’s lied about committing hundreds of murders. Is this one real – or a false confession?

Don and Kim zero in on serial killer Henry Lee Lucas. They find evidence in Summit Meadow that seems to match his story -- but is Lucas lying?

Hikers find a skull. Years later, Kim Tucker’s son Cullen takes on the case. After 40 years, Jane Doe is identified with new DNA technology.

We meet Jane Doe’s friends, learn about her family, life in a cult and other men who may have killed her. Investigators name their likely perpetrator.

An Alaska barista goes missing; cash is gone and surveillance video shows her walking away with a man. A text from her phone says she needs time away to think, but her dad is suspicious. Was she abducted? Police aren’t sure – until a ransom note arrives.

After a deposit to her account, the missing barista's ATM card makes a withdrawal. Video shows a masked man in a white Ford. A cop stops the car and finds her ATM card and phone, but no girl. Where is she? The man is arrested – but what has he done with Samantha?

The man, Israel Keyes, confesses to raping and killing the barista, torturing and killing a married couple in Vermont, raping the wife as well. Is his story true? Vermont cops search for the couple’s bodies to confirm, while the FBI asks him: who else have you killed?

Israel Keyes says he killed others but demands being promised the death penalty before saying who. Then guards find eleven skulls drawn in Keyes's own blood. Who are they? Before giving answers, Keyes suddenly shocks everyone with a dramatic and unexpected twist.