After a month-long scene investigation, investigators still donot know what caused the fire that led to a massive explosion atthe West Fertilizer Co. in Texas.

Authorities held a press conference late May 16 in West, Texas.They say they have narrowed the causes to severalpossibilities—crime among them—but they cannot be certain.

“At this time, the State Fire Marshal's Office and the [Bureauof Alcohol, Tobacco, Firearms and Explosives] are ruling the causeof the fire as undetermined,” says State Fire Marshal ChrisConnealy.

He says the investigation remains open to conduct moreinterviews and follow leads. Over 200 leads were developed and 400interviews were conducted thus far, say authorities.

More than 100 agents, investigators and experts have been on thescene since the fertilizer retailer exploded April 17 shortly aftera fire was reported at the site.

Ammonium nitrate stored at the site was the trigger of theblast, authorities have concluded. Hundreds of tons of thehighly-volatile chemical compound used to fertilize crops wasstored at the site.

The force and shockwaves from the explosion, which registered asa 2.1-magnitude earthquake and left a crater in the ground, leveledsome nearby homes and an apartment complex. It also severelydamaged a retirement center and a middle school. The explosionkilled 15 people, and hundreds were injured.

About 140 homes were damaged or destroyed. The Insurance Councilof Texas puts insured losses for this disaster at about $100million. The total includes insurance payments for WestFertilizer.

Adair Grain, parent company of West Fertilizer, has $1 millionof liability insurance on the site—no excess or umbrella coverage.The coverage was provided by a subsidiary of Crum &Forster.

Subsidiaries of W.R. Berkley Corp. filed suit against Adairshortly after the blast, alleging negligence. The Berkleycompanies insured individuals, businesses and churches in thesmall, rural town of about 2,800.

Berkley's attorney, Paul A. Grinke of McCathern in Dallas,previously told PC360 the lawsuit was filed in orderto “have a judge to go to” for an order like an injunction if, forany reason, the insurers were not allowed on the site to conduct aninvestigation. Insurers needed to wait for authorities to completetheir investigation before starting one of their own. Insuranceteams have been allowed on the site, but only to take pictures,Grinke says.

Grinke could not immediately be reached for comment.

Robert Champion, ATF special agent in charge, says investigatorsruled out many causes but several could not be eliminated: theelectrical system, a golf cart and arson.

About a week ago the Texas Department of Public Safety said acriminal investigation has been launched into the explosion. Theannouncement came shortly after a West paramedic was arrested forpossessing the ingredients of a pipe bomb. However, authoritieshave not linked the man to the explosion.

The ATF says it has spent nearly $1 million on the sceneinvestigation–$500,000 on rentals of heavy equipment to excavatethe facility.

The State Fire Marshal's Office says it continues to investigatethe deaths of a dozen firefighters who responded to the fire at theplant.