(Reuters) - Officials with the U.S. Chemical Safety Board say they may never know what caused last month's deadly fertilizer-plant explosion in Texas because of interference by federal and Texas agencies, according to a letter sent Tuesday by the head of the regulatory board to U.S. Senator Barbara Boxer.
The federal Bureau of Alcohol, Tobacco, Firearms and Explosives and the Texas State Fire Marshal's Office declined CSB access to witnesses and the explosion scene, wrote Rafael Moure-Eraso, chairperson of the safety board.
The ATF also failed to retrieve company documents that were scattered about the site, he alleged, and damaged evidence by using bulldozers and other heavy equipment to dig around the crater.
When the CSB finally did set up an interview with a plant employee, four armed ATF and State Fire Marshal's Office agents intercepted the employee and took him away before he could speak with CSB investigators, Moure-Eraso said.
ATF officials said Tuesday that all comments on the matter had to come from the Texas fire marshal.
The State Fire Marshal's Office said they would have a response to the complaint. As of early Tuesday evening, Reuters had not received the response.
Boxer, a California senator, could not be reached for comment.
The CSB is an independent federal agency responsible for investigating industrial-chemical accidents. The April 17 ammonium-nitrate explosion killed 14 people and destroyed a part of the town.
A site investigation like this usually takes several months, and heavy equipment should be used judiciously, said Hillary Cohen, spokesperson for the CSB.
"The site should have been carefully mapped and documented by all the investigative agencies," Cohen said. "Then it should have been systematically picked apart, with observation by all parties."
Cohen said local, state and other federal agencies have hindered the CSB in the past, but never for this long and never while altering the site to such a degree, Cohen said.
Moure-Eraso asked Senator Boxer to help compel the ATF to give the CSB access to the explosion site, debris collected from the site and mapping data of the crater caused by the explosion.
"To date the CSB has experienced significant obstacles that potentially compromise and delay our ability to complete the ‘comprehensive investigation' that you have rightly demanded, and that we would very much like to produce," he wrote.
Officials for the ATF and the Texas fire marshal said last week that the cause of the accident is undetermined and an investigation into a potential criminal cause is still ongoing.
The CSB is not aware of any evidence that the explosion was caused intentionally, Moure-Eraso wrote.
"All indications are that the event was an industrial accident within the CSB's investigative jurisdiction," he said.
(Reporting By M.B. Pell; Edited by Maurice Tamman)