After more than 40 years of searching, an international manhunt for Aribert Heim, a notorious doctor from the Nazi concentration camps and one of the most wanted Nazi war criminals, has zeroed in on a stretch of the Mediterranean coast of Spain, according to Spanish police officials.

Mr. Heim, born in Austria 91 years ago, is accused of torturing and killing hundreds of prisoners at the Mauthausen concentration camp in Austria in 1941 and 1942. The crimes for which he is sought include injecting gasoline into the hearts of victims, conducting operations on prisoners without anesthesia and executing prisoners just to record how long they took to die.

Spain has been a haven for Nazi war criminals since the end of World War II, when many were drawn here by the protection offered by the government of Francisco Franco, according to scholars of the issue.

Even after Franco died in 1975 and democracy was established, Spain's elected governments did little to cooperate with international searches for Nazi war criminals, those scholars said.

José María Irujo, author of "The Black List," a book about Nazis who fled to Spain, said in an interview that whole colonies of them lived here undisturbed for decades. "Many lived out their lives here, and died peacefully," he said.

"We are talking about hundreds of people," he said. "Spanish governments never did anything."