In 2014, YouTuber Kenny Veach set out to explore a mysterious M-shaped cave he had discovered near Nevada's Nellis Air Force Base in the Mojave Desert — then mysteriously vanished, never to be seen again.

A convicted pedophile who lived near JonBenét Ramsey at the time of her 1996 killing, Gary Oliva had a deep obsession with the six-year-old pageant star — and claimed responsibility for her murder in a series of prison letters.

In 2010, paroled killer Gregory Green married Faith Harris, the daughter of the pastor who’d advocated for his release. Years later, he murdered all four of her children in a fit of rage.

In May 1998, aspiring actress Brynn Hartman shot and killed her husband — then turned the gun on herself.

Although Dick Turpin's exploits were later romanticized in plays and serial fiction, in reality, he was a ruthless criminal who terrorized England in the early 18th century.

A 35-year-old auto repairman, Joey Buttafuoco began an illicit relationship with 16-year-old Amy Fisher in 1991 — and Fisher later tried to kill his wife.

Following her 2008 escape from the clutches of her father Josef, Elisabeth Fritzl now lives in a remote Austrian hamlet known only as "Village X" with her six children and new husband, Thomas Wagner.

After being imprisoned in Ariel Castro's home for a decade, Amanda Berry escaped her kidnapper in 2013 — and freed his other victims, Gina DeJesus and Michelle Knight.

Shanna "Liz" Golyar killed Cari Farver, her love interest Dave Kroupa's new girlfriend, in November 2012, then spent the next three years sending tens of thousands of text messages and emails posing as her.

Jessica McClure was playing in her aunt's backyard when she fell into a narrow well shaft in October 1987. And for the next 58 hours, the nation watched breathlessly as rescuers worked to free her.

Elizabeth Olten knew and trusted 15-year-old Alyssa Bustamante — but her "friend" turned out to be a thrill killer who had horrific plans for her.