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Jacobus Dirk HERTOGS





Classification: Serial killer
Characteristics: Kidnapping - Rape
Number of victims: 3
Date of murder: May 1979 - September 1980
Date of arrest: October 3, 1980
Date of birth: December 16, 1949
Victims profile: Tialda Visser, 12 / Emy den Boer, 18 / Edith Post, 11
Method of murder: Shooting - Beating
Location: Netherlands
Status: Sentenced to life imprisonment in 1981

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Jacobus Dirk (Koos) Hertogs (The Hague 16 December 1949) is a convicted Dutch serial killer. He was convicted for a total of three murders.


  • Tialda Visser, 12 years old, was reported missing on 11 May 1979, after she didn't return home after ballet classes at the Royal Conservatory of The Hague. Four days later, on 15 May, her lifeless body was found near the Leeghwaterbrug in The Hague. The cause of death could not be determined.

  • Emy den Boer, 18 years old, disappeared on 3 April 1980. She left her home in Schiedam to go to the Academie voor Lichamelijke Opvoeding in The Hague, however she never got there. Two days later, on 5 April, her body was found by a hiker in the forest near Nistelrode. She was shot in the stomach and head.

  • Edith Post, 11 years old, disappeared while at school on 29 September 1980. She left her class to get some materials from a closet in the hallway but didn't return. On 2 October her body was found in the dunes of Wassenaar. She was beaten to death, probably with a branch that was found next to her body.


After the murder on Edith Post, the police received an anonymous call with the information that Edith had bitten her murderer, and a bouncer of nightclub "De Nachtegaal" (The Nightingale) had a severe bite wound in his little finger. The bouncer was arrested and turned out to be Koos Hertogs. Police investigated his house and found blood traces of Tialda Visser and Emy den Boer. On the attic police found an isolated room. It is believed that Hertogs hid and raped his victims here for a period of time, before killing them. Koos Hertogs got sentenced to life imprisonment. Until 1989 Hertogs denied killing the girls. However after consultation with his lawyer he confessed so he could be placed on a lighter regime.

Sting operation

For a long time there were rumours that Hertogs had protection from higher hand. In the book Zuidwal, that tells the story of the serial killer, it is claimed that Hertogs got protected by Cornelis Stolk. An important judge and vice president of the court. However both men denied the claims.

In 2009 crime reporter Peter R. de Vries started a sting operation, trying to reveal if Hertogs murdered more people or if the claims made in the book were true. While being filmed with hidden cameras Hertogs, talking with a 'dear' friend, who turned out to be an infiltrant working voor De Vries, made some notable claims.

  • He admitted he kidnapped and murdered the three girls.

  • With the murder on Edith Post he had an accomplice.

  • Three times he had plans to murder someone, however the plans weren't carried out or failed.

    • A man he had an argument with fled inside a pool hall before Hertogs could kill him.

    • The director of a juvenile prison, however the man already died before Hertogs could carry out his plan.

    • A fellow inmate was lured into a trap, however a guard got suspicious and locked him up.

  • Confessed knowing who murdered the two Swedish women, Gun-Ingeborg Johannesson (18) and Ann Jönsson (19), in a forest near La Roche-en-Ardenne.

  • Confessed he had a special bond with judge Cornelis Stolk. Stolk paid for the driver's license of Hertogs and after an earlier conviction Stolk placed him under the care of a 'befriended' psychiatrist, who later turned out to be the ex-wife of Stolk. In the end of the television show it was revealed that Hertogs, in return, offered sexual services (oral sex) and child pornography to Cornelis Stolk. Mr. Cornelis Stolk died on 10 June 2004, aged 87.

Book "De zaak Koos H."

In august of 2012 writer and psychologist Patrick Oomens published the book " De zaak Koos H." He questions that Koos H. is a serial killer and concludes that he doesn't fit the profile. That sheds another light on the case and the writer shows that the whole case of Koos H. has more characteristics of a cover-up with connections to Gladio. With respect to the 'befriended' psychiatrist, the writer discovers that the ex-wife of Stolk wasn't a psychiatrist at all: but the first female pilot in the Netherlands who transported the Dutch Royal family in the early '50s.



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