It would sure be nice to know what exactly caused a fertilizer plant to explode in Texas last month, killing 14 people — especially given that 800,000 Americans live near similar facilities. But federal investigators are complaining to Congress that their work has been stymied by other government agencies, meaning the mystery might never be solved.

From The Dallas Morning News:

The U.S. Chemical Safety Board, in a letter released Tuesday, accused the Texas state fire marshal and the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives of hampering its work by blocking access to key witnesses for three weeks after the massive blast — “an unprecedented and harmful delay.”

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Board chairman Rafael Moure-Eraso wrote that the “incident site was massively and irreversibly altered under the direction of ATF personnel, who used cranes, bulldozers and other excavation apparatus in an ultimately unsuccessful quest to find a single ignition source for the original fire.” …

The chairman’s letter, dated May 17 and written in response to a request from [Sen. Barbara] Boxer [D-Calif.], is laced with frustration. Moure-Eraso pleads with the senator to intervene to help him and his team gain access to debris and other evidence removed by ATF and the fire marshal, along with West Fertilizer Co. records covering training of employees, chemical inventories and safety records.

“All indications are that the event was an industrial accident” rather than the result of arson, he wrote, questioning the rationale cited by ATF and the fire marshal for tightly controlling access to witnesses and evidence.

He described company documents “blowing around the site and exposed to rain and the elements. The ATF had no apparent interest in the documents.” Yet, he wrote Boxer, ATF agents refused to allow members of the safety board’s 18-person team in West to collect those documents.