About 20 suspects are sought by the authorities. Among the 15 held for questioning, some are not part of the Moirans traveller community camp.
“Hearings will start as soon as possible,” prosecutor Jean-Yves Coquillat told AFP on Monday.
“The searches led to the seizure of objects related to the investigation,”he added.
The police operation started at 6 am on Monday morning with about 300 police officers.
The incident occurred last October after authorities refused a jailed member’s request for a prison leave to attend his brother’s funeral who had died in an accident while riding in a stolen car.
But the judge had turned down the request, following which about 50 people of the traveller camp blocked off a road, torched 35 cars, some of which were thrown on the railway line between Grenoble and Lyon. This led to stopping of hundreds of trains.
They also ransacked a restaurant at the train station and the town hall.
The scenes resembled urban guerilla fighting. Authorities sent in 120 police and 100 firefighters to the small Alpine town of Moirans to bring the situation under control.
The mother of the young man who had died is part of the 15 held for questioning.