On September 29, 1980, eleven-year-old Edith Post, the daughter of a deputy fire brigade commander, left her classroom at the Wethouder Huybregtse school in Wassenaar to fetch something from the needlework cupboard in the corridor, and did not come back. On October 2 a walker found her body in the dunes at Wassenaar. She had been beaten to death with something heavy, probably the branch lying beside her. Then an anonymous caller told the police that Edith had bitten her killer, and that the doorman of a nightclub called De Nachtegaal had a bad bite wound on his little finger. On October 3 they arrested Jacobus Dirk Hertogs, known as Koos.
In his house on the Zuidwal in The Hague they found blood traces from two other girls and, in the attic, a small, very well insulated room fitted out as a torture chamber. Police believed he had abused and killed his victims there. He also had booklets of child pornography in the house, though experts who studied him concluded that he was not a pedophile and had taken young girls for practical reasons, because they were easier to control than grown women.
The first was Tialda Visser, twelve, who on the afternoon of Friday, May 11, 1979, left the Royal Conservatory in The Hague, where she took ballet and played three instruments, to take the tram home. She was reported missing that day. On May 15 her body was found by the Leeghwater bridge in the Laakhaven district. She had been sexually assaulted and injured with a sharp object, and there were strangulation marks on her neck. The pathologist recorded drowning; other accounts say the exact cause could not be established, and some give the date of the discovery as May 14.
Emy den Boer, eighteen, left her parents' house in Schiedam on the morning of April 3, 1980, for The Hague, where she was training at the Academy of Physical Education. She never arrived. Two days later a walker found her body in woods near Nistelrode in Brabant. She had been shot in the stomach and the head. Hertogs's girlfriend later testified that the two of them had been in bed when they heard noises from the attic, that he went up in a rage, and that she then heard two shots.
He was born in The Hague on December 16, 1949, into a Catholic family of seventeen children, sixteen of whom grew up. He was so unmanageable as a boy that at sixteen he was placed in a juvenile custodial order. Before the murders he had been jailed for driving without a license, burglary, armed robbery and drug dealing; in all he was convicted twenty-six times, and by the time he was sentenced to life he had spent about fifteen years in institutions and prisons. A detective on the case has said a woman in Voorburg who rang the police after seeing him watching through binoculars is part of why they caught him so quickly.
His trial opened on October 13, 1981. Forty journalists attended, and marksmen lay on the roof of the courthouse in The Hague for fear of an attempt to free or kill him. He denied everything. He told the detectives that if he ever got out he would come for them, or their wives and children. In November 1982 the court sentenced him to life for the abduction, abuse and murder of the three girls, and the sentence was upheld on appeal.
He went on denying the murders until 1989. Then, after consulting his lawyer, Wim Anker, he made a partial confession so that he could be admitted to a forensic psychiatric clinic, and until 2006 he was held at the Van Mesdag clinic in Groningen, after which he was sent back to prison. He spent his last years on a long-stay ward at the prison in Vught. He died in a hospital in 's-Hertogenbosch on July 19, 2015, at sixty-five, by then the longest-serving life prisoner in the Netherlands.
In 2009 the crime reporter Peter R. de Vries began an investigation using an informant, Hertogs's childhood friend Nico van Empel, who renewed contact with him. Hertogs went to court to stop the letters and recordings being made public. The first broadcast, on April 4, 2010, went ahead because it used no secretly made footage, and prompted questions to the justice minister. On April 9 a judge barred the hidden-camera footage from the next episode on pain of a 15,000-euro penalty; De Vries, SBS Broadcasting and Endemol showed it anyway, and De Vries lost an appeal on March 8, 2011. On the hidden camera Hertogs admitted abducting and killing Tialda Visser, Emy den Boer and Edith Post, spoke of an accomplice in the Post murder whose name was obscured, and described three murder plans he had not carried out. The third broadcast repeated a claim made earlier in Sytze van der Zee's 2003 book about the case, Zuidwal: that as a young prisoner he had had an unusual relationship with Cornelis Stolk, then vice-president of the court in The Hague, who was said to have paid for his driving lessons, found him a better lawyer and once secured his acquittal, and to whom Hertogs was said to have offered sexual services and child pornography. The book raised the question of protection from above; none of it was ever tested in court.
Police suspected him of four to six other murders, among them a seventeen-year-old girl found on a garbage dump in Brabant in 1977, two Swedish tourists shot dead in woods in Belgium in May 1980 who had been seen with him, and two cases from 1972 and 1975. He denied the Belgian killings while saying he knew who had done them. Prosecutors brought only the cases they judged provable, since three were enough for a life sentence.