In 1976, Herman Knippenberg, a 31-year-old Dutch diplomat, received a letter from the relative of two missing backpackers.
The two backpackers, Henk Bintanja, 29, and his fiancée Cornelia Hemker, 25, had stopped communicating with their families.
Shortly afterwards, Bintanja and Hemker's bodies were found burnt on the side of a road near Bangkok, Thailand, leading Herman Knippenberg on a years-long investigation into their deaths.
It was this investigation that led Knippenberg to discover that the couple had been burned alive by Charles Sobhraj – one of Asia's most wanted criminals.
Watch the trailer for Netflix's The Serpent below. Post continues after video.
In the years that followed, Knippenberg dedicated his life to finding incriminating evidence against Sobhraj in an attempt to have the serial killer arrested.
"I couldn't forget him, it was like having malaria," Knippenberg later told The Nepali Times.
"Every couple of years or so something would happen that would draw me back into the case again."
Now, decades later, new Netflix series The Serpent is recounting Herman Knippenberg and his then-wife Angela Kane's search to unveil the serial killer.
Starring Tahar Rahim, Billy Howle, and Jenna Coleman, the eight-part series is inspired by the true story behind the pursuit of Charles Sobhraj and his accomplices.
Is The Serpent a true story?
In the 1970s, Charles Sobhraj, best know as 'The Bikini Killer', preyed on Western tourists who were travelling through the "Hippie Trail" of Southeast Asia.
During that time, Sobhraj is believed to have been responsible for between 12 and 24 murders.