Probably arson done by a disgruntled ex-employee.

From the article:
News: We have been told by a source that certain machines were moved from the factory last week, and some employees let go.

Yeah, GRP was either downsizing and laying ppl off, or relocating and laying ppl off.

Article Update: The newspaper reports that the fire broke out in the factory's boiler room, an off-duty police officer spotted smoke, passed by the front of the building where one of the Gandini owners were, they went together to locate the source of smoke and found a broken window to the Boiler room.

If this happened late at night, it was convenient that a Gandini owner was there, huh? *cough* insurance fraud *cough*

Still, sucks for the employees and the loss of Massa's old race car.