DNA found on the boy's pyjamas was of male origin. But no samples in Dutch and international criminal databases matched it. Nor did hundreds of samples initially taken from men living near the nature reserve and from men linked to Nicky or the camp. A Dutch law passed in 2012 allowed for a practice known as familial DNA profiling, which involves taking DNA samples from people who could potentially be relatives of a suspect, based on geographic and social profiles. Marker for murdered Dutch boy Nicky Verstappen. Credit:Wikicommons/Saschaporsche The hope, said Nicky Jansen, a spokeswoman for the Dutch Forensic Institute, which carried out the analysis, is that "if the DNA of a volunteer shows any familial relationship to the suspect's DNA, investigators can identify the suspect by analysing the volunteer's family tree." The technique opened new doors for the investigation into the murder of Nicky. In 2013, a Dutch prosecutor ordered two new DNA sampling investigations: the voluntary sampling of Dutchmen based on familial profiling, and the obligatory sampling of 1500 men of special interest to the case.

Eventually, 17,500 Dutchmen volunteered to provide DNA for the investigation. None matched the original sample. Yet when one person of special interest — Jos Brech, a 55-year-old Dutchman who had been missing since April — failed to show up for obligatory sampling this year, investigators dug deeper. Police took DNA samples from Brech's family and his clothes at his mother's home, about 15 km from the crime scene, and pulled DNA from a parallel inquiry into his disappearance. All matched the DNA found on Nicky's pajamas in 1998. Last week, investigators publicised the suspect's identity. And within days, a tip led them to an abandoned house near Castellterçol, outside Barcelona, said Judith Verbaan, a police spokeswoman in Limburg province, where Nicky was killed. Spanish police arrested Brech there Sunday. Spanish authorities said they had arrested him while he was cutting wood in a field. Among his belongings were survival items like fishing instruments, a book on edible wild plants, dried food, boots and mountain gear, and batteries, police said.

Brech is a member of a Dutch bushcraft club, where members share experiences about living in the wild. Since he went missing this April, investigators said, Brech had lived in outdoor shelters and abandoned houses across Western Europe. The Dutch public prosecutor's office said it expects Brech to be extradited soon — within a week if he cooperates, officials said. If he appeals, a Spanish judge will have 90 days to rule on the extradition. Speaking to reporters Monday, Nicky's mother, Bertie Verstappen, thanked the Dutch authorities, investigators, the media and in particular a Dutch crime journalist, Peter de Vries, for having continued to ask questions over the years. "I don't dare to call names, out of fear to forget someone, but all those people who gave DNA, who looked around, who called around, I am so grateful to them," she said tearfully of Brech's arrest. "Now, I hope he will talk, so we'll get answers to our questions." New York Times