There was also a hammer attack in 2017 by an alleged ISIS doctoral student against a cop. Also a knifing leaving two people dead by a mentally ill man who spoke of terrorism in 2018.

-https://www.npr.org/2018/08/23/641152018/2-killed-in-knife-attack-outside-paris
https://www.cbsnews.com/news/notre-dame-shooting-paris-police-confirm-incident-warn-public-to-stay-away/

The official response is to treat the fire today as an accident [ruling out arson and terrorism] for now. The additional words "for now" used my many news agencies is interesting choice of words. At best, it means they haven't ruled out arson, and terrorism completely. But the french prosecutors office specifically said there was no arson and no terrorism.
So where did the words "for now" come from, and what does it mean. One could construe those words ("for now") for virtually any theory, which is worrisome. For example, one possible theory could be do they know it was an arson, but it isn't politically convenient to say that given the people are already in the streets protesting the macron government. But...there was no arson according to the prosecutor. The "for now" thus is rather cryptic.
Conspiracy theories brew the most when the people have no reason to believe the government and the news media. But this places more pressure on these agencies to give answers. And surely the "for now" could be an invitation down the rabbit hole.
https://www.washingtontimes.com/news/2019/apr/15/notre-dame-arson-terrorism-ruled-out-now-paris-pro/

I suppose the biggest reason for doubt of at least arson is the lack of anyone claiming responsibility.