BRUSSELS — For 20 years, the Dutch police investigated the rape and murder of an 11-year-old schoolboy, and the Dutch news media chronicled the case’s many twists and turns.

Now, after an investigation in which 17,500 Dutchmen voluntarily took part in DNA profiling, a suspect has been arrested in Spain.

The boy, Nicky Verstappen, had attended a summer camp at a nature reserve in the southern Netherlands in 1998. On a night that August, he left his tent and never returned. His body, pajama-clad and barefoot, was discovered the next day, hidden in a dense pine forest about a mile away. He had been raped and killed.

DNA found on the boy’s clothes 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.