I've been trying to find out more, seems they are not saying much about the incident - and to be honest rightly so.
Where is the evidence of these 'fires'?
It's reported, reading Le Monde, some of the damage was from fire, some from cutting.
There is a criminal investigation into the damage and various other possible offences, attack on the national interest, data infrastructure and so on. Wider investigations coordinated by their anti-terrorism people.
Their structure is that their equivalent of our CPS ('parquet' and magistrates) runs the investigation from the start as well as the prosecution, although the legwork is done by the police forces (gendarmerie, police nationale plus police judicaire branch). The national organised crime prosecutors are in charge. My impression is that the parquet say little until they have a complete case, equivalent of charging here. Reported that 50 investigators are working already.