According to the police, 31 Aarhus Muslims, all of them under the age of 30, have traveled since late 2012 to Syria to support forces battling the government of Bashar al-Assad, but only one of them went this year. Five of these are believed to have been killed, including two women, and 16 have so far returned home.

“What we are doing seems to be working,” said Jorgen Ilum, the chief of police for the region, describing the program as a “crime prevention” exercise that seeks to “protect society from extremists,” not to mollycoddle jihadists. The police chief acknowledged that full “rehabilitation” of returnees is extremely difficult, and that “none of them are completely normal,” but added that none had veered off into militancy since coming home.

Fears that former fighters may run amok in their home countries have been intense since Mehdi Nemmouche, a 29-year-old French Muslim, killed four people at the Brussels Jewish Museum in May after spending a year in Syria.

A 2013 study by Thomas Hegghammer, a researcher at the Norwegian Defense Research Establishment, involving 945 jihadist fighters who returned from previous conflicts in Afghanistan, Bosnia and elsewhere, found that a maximum of one in nine former fighters came home to plot or carry out attacks in the West. Mr. Hegghammer, in a telephone interview, said the rate for returnees among the approximately 3,000 Europeans who have gone to Syria to fight was, so far, much lower.

In Aarhus, the returnees are screened by the police with help from the domestic security service, known as P.E.T., but so far none of the 16 who came home have been arrested. Instead, they have been offered a “mentor” whose task it is to convince them that militancy has no place in mainstream Islam.

Preben Bertselsen, a psychology professor at Aarhus University whose theories help underpin what is known as the “exit program for radicalized citizens,” said returnees had “lost their moral compass” but “only become ticking bombs if we don’t integrate them” back into society. Aarhus’s approach, he said, aimed to prevent criminal acts by former fighters, not to purge their beliefs. “I am not the political or religious police,” he said.