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.
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.
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.