Updated

A court on Thursday acquitted a subsidiary of French oil giant Total and a former factory chief in a 2001 explosion at a chemical plant that killed 31 people and left more than 2,000 injured.

The court in Toulouse, in southwest France, acquitted the former chief of the AZF chemical fertilizer plant, Serge Biechlin, and Total subsidiary Grande Paroisse after a nine-month trial, citing "reasonable doubt" because there was no direct proof that they were responsible for the explosion.

No one has been convicted in the blast that tore apart the chemical plant with the force of a magnitude-3.4 earthquake. It came 10 days after the Sept. 11 terror attacks in the United States, raising fears at the time of a link with terrorism.

Both Biechlin and the company had been charged with manslaughter, involuntary injury and destruction of property. Biechlin had faced up to three years in prison and Grande Paroisse a $334,000 fine.

The explosion occurred in a hangar containing 300 tons of ammonium nitrate. The chemical, which was produced at the plant, can be used in both fertilizer and explosives.

The blast blew out windows in homes and buildings miles away and scores of schools were damaged.

The trial drew intense interest in Toulouse, and the verdict was presented in a municipal hall with some 750 people present.

In a 2006 report, judicial investigators blamed the explosion on negligence that allowed ammonium nitrate to come into contact with other chemicals. In June, prosecutor Patrice Michel cited "grave dysfunction in the organization and managing of waste," in organization of work and varying treatment of salaried workers and subcontractors.

However, Presiding Judge Thomas Le Monnyer said the causal link between organizational errors and the damage is "uncertain."

"There is a rupture in the causal chain," he said.

In another decision Thursday, the court cleared Total and its former chief Thierry Desmarest of any responsibility. At one point, Desmarest was called to testify but he was never charged.

Victims' groups and their families, who were civil parties in the case, said they were frustrated by the verdict and at least one said it would appeal.

"The scene was set for a guilty verdict and yet the court didn't reach one, I believe, because of an excess of scruples," said Stella Bisseuil, lawyer for the Association of Grieving Families.