A volunteer detained for questioning over a fire at the Saint-Pierre-et-Saint-Paul cathedral in Nantes has been released without charge.
The blaze tore through the cathedral early on Saturday morning, destroying stained glass windows and the grand organ inside.
The detained Rwandan refugee, 39, was in charge of locking up the building the day before the fire.
The Nantes public prosecutor said the man was freed on Sunday evening.
Pierres Sennès said the authorities had wanted to clear up any inconsistencies and that the questioning was a "normal procedure".
The volunteer has not been named.
Mr Sennès said the fire is believed to have been arson. Three fires were started at the site and an investigation is now under way.
Quentin Chabert, the lawyer for the refugee, said at the time of detention there was "nothing at this stage to link my client to the fire" and that the investigation must go on "with respect for everyone's rights and in particular those of my client".
Jean-Charles Nowak, a clerk at the cathedral, told French newspaper Le Figaro the volunteer was "a man of duty" who had "suffered a lot in Rwanda" - a country he left several years ago. The refugee had been discussing extending his visa with local officials, he said.
"I don't believe for a second that he could have set the cathedral on fire. It's a place he adores," Mr Nowak said.
About 100 firefighters managed to stop the flames from destroying the main structure at the cathedral on Saturday. French Prime Minister Jean Castex praised their "professionalism, courage and self-control".
The fire comes over a year after a blaze nearly destroyed Notre-Dame Cathedral in Paris.
Earlier this month, French President Emmanuel Macron announced its iconic spire would be rebuilt exactly as it was, ending speculation it would be changed to a more modern style.