We can go back and forth, but fact remains, it was declared an accident. But the cause in written media was sometimes cigarette, then it was short circuit, then the control computer had a bug and fire was not located in the right spot, welding was the cause, etc. But as the live footage was shown they said that the officials have said, it was an accident.
It is always talked about as an accident from the official side. No one brought any evidence for it and in all seriousness, firefighters and investigators usually need some time to find the cause and before they say if something is an accident or arson.
This cathedral is a symbol of France and such lack of enthusiasm to find the cause of fire from the official side is very surprising in the most negative way.
It should not be forgotten that the only people rejoicing of the fire were mohammedans as they were at 9/11.