Paris (AFP) - French prosecutors on Tuesday opened an investigation into negligence over a devastating fire at a chemicals factory in northern France last month that affected farmers and left local residents complaining of breathing problems.
The fire at the Lubrizol plant just outside the French city of Rouen saw some thousands of tonnes of chemical products burned and acrid smoke spread some 22 kilometres (14 miles) from the site.
Paris prosecutor Remy Heitz said in a statement that an investigation had been opened into "involuntary destruction caused by fire due an obviously deliberate breach of a security obligation".
The investigation has been handed to three investigating magistrates in Paris who can then decide whether to press charges.
So far the investigation is only against "X" which in France's legal system means that no individual or institution is yet being targeted.
The statement said that despite a search of Lubrizol offices, the interviewing of some 100 witnesses and taking of samples it has not yet been possible to determine the origin of the fire.
The Lubrizol plant is owned by US billionaire investor Warren Buffett and makes industrial lubricants and fuel additives.
The September 27 fire proved a tipping point in public anger over environmental risks, especially after the lead contamination sparked by the April 15 fire at Notre-Dame cathedral in Paris.
The government at one point banned the harvesting of crops or the sale of animal products from a wide swathe of tainted countryside surrounding Rouen, a decision affecting more than 1,800 farmers whose fields.