FREDERIKSTAD, Norway — The real trouble started when they stopped causing trouble. Torleif Sanchez Hammer and his friends — all residents of the same small cluster of clapboard houses in southern Norway — had been having run-ins with the police for years but then suddenly halted their marijuana-fueled gatherings in the basement apartment of Mr. Hammer’s widowed mother.
Police officers in this placid Norwegian town had busted their marijuana parties so regularly that “we knew them all on a first-name basis,” recalled Ragnar Foss, head of a local police unit responsible for youth crime. But, two years ago, they cleaned up their act. “We wondered what had happened but were glad when they dropped off our radar,” Mr. Foss said.