Detectives looking for clues into the disappearance of Holly Maddux made a grisly discovery while searching the apartment she'd left 19 months earlier

Texas beauty Holly Maddux vanished in 1977 just as she was breaking up with her long-time boyfriend, Philadelphia-based activist Ian Einhorn.

The 30-year-old former high school cheerleader and salutatorian met the hippie leader in 1972, during the height of the Vietnam War, when she joined thousands of other young Americans in embracing the counter-culture ideas of the day.

Taken by Einhorn’s charisma and vision for the future, the gentle, soft-spoken Bryn Mawr College graduate fell fast and hard for the man, whose friends included Grateful Dead singer Jerry Garcia and radical activist Abbie Hoffman. They moved in together as he introduced her to a life far removed from her childhood in traditional East Texas.

But the excitement of the relationship wore thin, and after enduring five stormy years with Einhorn, she decided in 1977 to break up with him when she met another man who was his polar opposite.

After assuring her new boyfriend she would be back soon, Maddux went to Einhorn’s Philadelphia apartment to retrieve her belongings. She was never seen alive again.

The mystery surrounding Maddux’ disappearance and the shocking truth about her death are examined in-depth on tonight’s episode of People Magazine Investigates on Investigation Discovery. The episode, titled “The Unicorn Killer,” airs at 10 p.m. ET. (An exclusive clip is shown above.)

Einhorn Extradition
Holly Maddux, who vanished in 1977 and whose family sought justice for her murder for decades.
| Credit: William Thomas Cain/Getty Images

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The episode chronicles the unlikely twists and turns of the high profile case, including an international manhunt for her murderer, dubbed “The Unicorn Killer'” — and the decades-long quest to seek justice for Maddux.

A key event took place on March 28, 1979, when detective Michael Chitwood headed to Einhorn’s Philadelphia apartment with a warrant to look for the answers authorities had been seeking since Maddux vanished.

“We wanted to gather as much forensic evidence as we could find,” Chitwood says in the episode. “I knew where I wanted to go and that was the closet.”

The closet sat above the spot where neighbors in the apartment below had reported seeing a liquid that had dripped down into their home — and left a horrific smell.

People Magazine Investigates: The Unicorn Killer, airs tonight at 10 p.m. ET on Investigation Discovery.