French reports say the fire was found just minutes after closing for tourists.
Perhaps a backpack secreted in a corner with some phosphorus in a glass jar? Remove the lid and let it smolder in the pack?
I read that in a spy novel book once.
Smell comes first...
Don’t they have security to check backpacks?
The burning of Notre Dame Cathedral happened on the same day as the Boston Marathon bombing on April 15, 2013, when two homemade pressure cooker bombs detonated by cell phone signals. It would be easy to set off a fire ignition device using a cell phone.