A volunteer at the Saint-Pierre-et-Saint-Paul cathedral in Nantes has been detained after a fire tore through the building, officials say.
The Rwandan refugee was in charge of locking up the day before the blaze destroyed stained glass windows and the grand organ inside.
A lawyer for the man said there was “nothing to link” him to the fire.
Prosecutors said they wanted to clear up inconsistencies and that it would be “premature” to think he had a role.
“We must remain careful as to the interpretation of this police custody. It’s a normal procedure,” public prosecutor Pierres Sennès said. 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 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”.
- In pictures: Fire hits ‘Gothic jewel’ of Nantes
Jean-Charles Nowak, a clerk at the cathedral, told French newspaper Le Figaro the volunteer was “a man of duty” who has health problems and “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.