By Audrey Sommazi, Associated Press Writer

TOULOUSE, France (AP) — A subsidiary of French oil giant Total and a former factory director went on trial Monday for an explosion at a chemical plant eight years ago that killed 30 people and injured thousands.

The explosion at the AZF chemical fertilizer plant in Toulouse jolted southwest France with the force of a 3.4 magnitude earthquake, but its cause remains unexplained. The timing, ten days after the Sept. 11, 2001, terrorist attacks in the United States, immediately raised fears that it was a criminal act.

But investigators say they have largely ruled out terrorism and are nearly certain the explosion was an accident.

Plaintiffs in the criminal case hope the trial will shed light on the cause of the blast, which 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 explosion caused injuries and blew out windows in homes and buildings miles (kilometers) away. Scores of schools were damaged.

Total, whose subsidiary Grande Paroisse owned the plant, "isn't leaning toward any theory" about the cause, said Patrick Timbart, a locally based executive for the oil giant.

About 200 people gathered outside the courthouse in Toulouse as the trial began, police said. Others held a silent march near the plant at the "Sept. 21" traffic circle, named for the date of the explosion.

In a 2006 report, judicial investigators blamed the explosion on negligence that allowed ammonium nitrate to come into contact with other chemicals.

The plant's director at the time, Serge Biechlin, and Grande Paroisse face charges that include manslaughter and involuntary injury and involuntary destruction of property. Under French law, companies can stand trial as legal entities.

Biechlin, faces up to three years in prison, as well as possible fines. Grande Paroisse faces up to euro225,000 ($288,000) in fines. Timbart said Total has already spent euro2 billion out-of-court in compensation for injuries and material damage.

Daniel Soulez-Lariviere, a lawyer for Biechlin and Grande Paroisse, said it appears impossible that the explosion was an accident and his clients should be acquitted.

"The charges in this trial are based mostly on experts' reports that are inaccurate," Soulez-Lariviere said.

Gerard Ratier, the head of an association representing victims of the blast, said he thought Total had not come clean and he hoped the trial would force the company to "stop camouflaging the truth."

Some 200 witnesses and experts — including Total's then-CEO, Thierry Demarest — are expected to testify. The trial is expected to last from three to four-and-a-half months.

The court has set aside time to hear arguments on various theories — from a meteorite strike to a terrorist plot.

More than 1,200 people sought compensation from Total and its subsidiary for damages including injuries and destruction of property.