The U.S. Chemical Safety Board (CSB) says a turf war is hindering its investigation into the April 17 West, Texas fertilizer plant blast.

In a letter to Sen. Barbara Boxer (D-Cal.), CSB chairman Rafael Moure-Eraso accused the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) of destroying and  withholding evidence and refusing to permit CSB investigators access to the site.

Boxer chairs the Senate’s Environment and Public Works Committee, which plans to hold hearings on the explosion, which killed 15 and injured 200. It also destroyed or damaged dozens of buildings in West, a small, close-knit town north of Waco.

Referring to the ATF’s rationale for its handling of the situation, Moure-Eraso said the tight controls were unwarranted. “All indications are that the event was an industrial accident” – not criminal activity, as initially suspected by the ATF.

Moure-Eraso said the ATF had destroyed vital evidence by using cranes, bulldozers and other large equipment to sift through debris “in an ultimately unsuccessful quest to find a single source for the original fire.”

The ATF denied access to the site to two CSB members. It also withheld West Fertilizer Co. documents from CSB investigators – items which were “blowing around the site and exposed to rain and the elements. The ATF had no apparent interest in the documents,” said Moure-Eraso. He asked Boxer to intervene to get the CSB more access to evidence.

Of interest to the Board: company employee training and chemical inventory records.

Despite the conflicts with other agencies, the CSB has said it hopes to release a final report in 12 to 18 months.