DAKAR, Senegal — Dozens of schoolgirls from the northern Nigerian community of Dapchi were returned early Wednesday morning, dropped off by the same group of Boko Haram militants who kidnapped them more than a month ago as they offered a stern warning to never go back to school again.

The surprising turn of events was greeted with joy from parents whose daughters were safely returned, but the relief was tempered by suspicions that several girls had died while in the hands of the militants. At least one is apparently still being held.

Jauro Usman, a resident of Dapchi who is close to many of the parents of the kidnapped girls, said those who had been reunited were “very, very happy.”

“Boko Haram came themselves and dropped our daughters,” he said.

The return of the girls might wind up as a major propaganda coup for Boko Haram as villagers had been outraged at the way Nigerian officials had handled the girls’ capture, and some questioned why the military did not launch a rescue operation.