From diplomat to detective, this man helped bring Asias notorious Serpent killer to justice

The smell inside the morgue was overpowering, as disinfectant masked the odor of decaying corpses.

"It's them," said a dentist, who had just inspected the mouth of a stiff body.
Light from a window at the back of the room illuminated who she was talking about: two badly burnt bodies that had been opened for an autopsy and stitched back together with surgical cable. The woman's brain had been bashed in with something heavy and the man strangled, a pathologist said. Both were still alive when they were set alight.
The scene at the police mortuary in Thailand's capital, Bangkok, on March 3, 1976, remains clear in the mind of former Dutch diplomat Herman Knippenberg. He says it was the most shocking thing he saw in 30 years of foreign service, and sparked a decades-long personal endeavor to bring the alleged killer to justice.
"I had the feeling that I was stepping outside of myself -- that I'm on the side, watching the scene," he recalled in an interview earlier this year.
Knippenberg would later learn the Dutch couple in the morgue were among at least a dozen people Charles Sobhraj admitted to killing -- though he later recanted. "The Serpent," a new BBC/Netflix drama series coming to the streaming service in April, tells how for years, Sobhraj evaded the law across Asia as he allegedly drugged, robbed and murdered backpackers along the so-called "hippie trail" -- and how for years, Knippenberg worked with authorities to capture him.
Sobhraj is now serving a life sentence in a Nepalese jail for killing two tourists in 1975. But many of his alleged murders remain unresolved -- and for Knippenberg, the case still doesn't feel completely closed.

In 1976, Bangkok hadn't yet developed into the metropolis of towering skyscrapers it is today. The subway and Skytrain were yet to be built and bumper-to-bumper traffic meant it could take hours to travel across the hot, crowded city.
Unlike today's era of instant communication, it was a slower, less connected world. There were no smartphones or social media, and a missing traveler could go unchecked for weeks, maybe even months.
On February 6 that year, Knippenberg received a letter about two Dutch backpackers who had done exactly that.
It was from a man in the Netherlands who said he was searching for his missing sister-in-law and her boyfriend. Henricus Bintanja and Cornelia Hemker had been "ardent correspondents," writing to their family twice a week as they traveled Asia, the letter writer said. But for six weeks, the family had heard nothing.

At the time, Knippenberg thought his friend had lost it. The story seemed too outlandish.
But as both men would later discover, Alain Gautier was one of multiple aliases used by Sobhraj.
On the run and posing as a gem dealer in Bangkok, the French thief, conman and killer had for years been befriending travelers -- then drugging and robbing them. In a time of laxer border security, he often adopted his victims' identities and used their stolen passports to zigzag across Asia.
Searching for 'the Serpent'
The day after his trip to the morgue, Knippenberg called Siemons and demanded to know where he'd heard about the gem dealer. After some persuading, Siemons gave him a name -- Nadine Gires, a Frenchwoman who lived in the same Bangkok apartment building as Sobhraj, and who introduced clients to him.
Upon meeting Knippenberg, Gires revealed how other people working for Sobhraj had fled after finding a collection of passports belonging to missing people, fearing he'd killed them. She also said she remembered seeing the Dutch couple come to his home.
Knippenberg alerted the Thai authorities, but also continued his own inquiries.