Agence France-Presse reported that the unnamed volunteer, who had been an altar server, was responsible for closing the Cathedral of St. Peter and St. Paul on the night of the fire, which arson investigators said appeared to have started at three different points in the cathedral.
The volunteer had been detained by French police on the day of the suspected arson and questioned about alleged inconsistencies in his schedule, but was released without charge the following day.
However, developments in the arson investigation led the volunteer to be rearrested, indicted, and detained in pre-trial custody on July 25, according to the prosecutor.
The fire at the 15th century Nantes Cathedral of St. Peter and St. Paul destroyed the Gothic church's great organ and 16th century rose window. Scheduled Masses and a series of summer organ concerts at the cathedral have been moved to other churches in the diocese.
"For the Catholic community, this disaster is greeted with great sadness. The vocation of the mother church of the diocese is to bring it together in unity around its bishop. Everyone is at home here. How can we not think of our future bishop, who cannot be installed in his cathedral?" Fr. Francois Renaud, administrator of the Diocese of Nantes, said in a statement July 22.
Renaud said that much of the costs of the damage to the cathedral will be assumed by the French government, which owns the building. However the diocese will be responsible for replacing the cathedral's damaged pews and is seeking donations for the construction of a new organ.