Jacobus Dirk Hertogs, known as Koos, was born on December 16, 1949. He worked as a doorman at a nightclub in The Hague called De Nachtegaal and had a long criminal record. He lived on the Zuidwal in the city with his girlfriend.
On the afternoon of Friday May 11, 1979 twelve-year-old Tialda Visser left the Royal Conservatory in The Hague, where she took ballet lessons and played three instruments, to catch the tram home. Her body was found a few days later in the Laak, in the Laakhaven district. She had been sexually assaulted and injured with a sharp object; there were marks of strangulation on her neck. The pathologist recorded drowning as the cause of death, and other accounts say the cause could not be established. Reports give the date of the discovery as either May 14 or May 15.
Emy den Boer, eighteen, left her parents' house in Schiedam on the morning of April 3, 1980 for her college in The Hague and never arrived. A walker found her body two days later in woods near Nistelrode, in Brabant. She had been shot in the stomach and the head. His girlfriend later gave evidence 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.
Edith Post, eleven, was the daughter of a deputy fire brigade commander. On September 29, 1980 she left her classroom in Wassenaar to fetch materials from a cupboard in the corridor and did not come back. Her body was found on October 2 in the dunes at Wassenaar. She had been beaten to death, probably with a branch found beside her.
An anonymous caller told police that Edith Post had bitten her killer, and that a nightclub doorman had a bad bite wound on his little finger. Hertogs was arrested on October 3, 1980. A search of the house on the Zuidwal found blood matching Tialda Visser and Emy den Boer, and an insulated room in the attic, which the Dutch press has called the torture room ever since. Investigators believe he kept his victims there. A detective on the case has said publicly that a woman in Voorburg who rang the police after seeing him watching through binoculars is the reason they caught him as quickly as they did.
The trial opened on October 13, 1981 under heavy security. He denied everything. The court found the three murders proved and sentenced him to life in 1982, and the sentence was upheld on appeal. He threatened the detectives during the investigation, telling them that if he ever got out he would come for them, or their wives and children.
He kept denying the murders for years after his conviction. Accounts differ over when that changed: some say 1989, on his lawyer's advice and in the hope of an easier regime, and Dutch news reports say a partial confession in 1997, after which he was moved out of prison into a secure hospital. He was returned to a secure individual treatment unit at Scheveningen in 2005 and ended up on a long-stay ward. In 2010 the crime reporter Peter R. de Vries broadcast recordings made secretly inside the clinic by a man who had got close to him, in which he described his part in all three killings.
Police suspected him of between four and six other murders, among them a seventeen-year-old girl found on a rubbish dump in Brabant in 1977, two Swedish tourists shot dead in woods in Belgium in May 1980 who had been seen in his company, and two earlier cases from 1972 and 1975. He denied the Belgian murders while saying he knew who had committed them. Prosecutors charged only the cases they judged provable, on the basis that three were enough for a life sentence.
He died in custody in July 2015, aged sixty-five, by then the longest-serving life prisoner in the Netherlands. The journalist Sytze van der Zee published a book about the case in 2003 under the name of the street he had lived on.