I read that the renovation involved removing and refurbishing bronze statutes in the area of the spire. Removing the statues left gaps in the structure that allowed access to the timbers supporting the roof.
If that is accurate, then all construction workers have to be investigated. Could be a simple accident like someone throwing a cigarette butt in that smoldered or it could a complicated arson plot such as a timed device set to explode/ignite after work hours.
Have to check how construction workers got access to the site, and if ID was required. Did they have secured access? Could be an arsonist who disguised himself as part of the work crew mingle in unnoticed. Who knows until that question is asked and answered?
I don't think any type of speculation or premature official announcement will be believed. If Macron tries to pull a news shutdown like in NZ it will backfire. He's on a tightrope with this one. Done for he be if muzzie planned desecration is involved, hfor sure.