RENNES : A volunteer church assistant has confessed to setting the fire that severely damaged a Gothic cathedral in the western French city of Nantes, his lawyer said Sunday, though his motives remain a mystery.

The 39-year-old, an asylum-seeker from Rwanda who has lived in France for several years, was arrested Saturday after laboratory analysis determined that arson was the likely cause of the blaze, the local prosecutor's office said.

"My client is cooperating," lawyer Quentin Chabert said at a news conference in Nantes, without speculating what prompted the attempt to burn down the Cathedral of Saint Peter and Saint Paul.