Dozens of investigators have spent several weeks excavating the blast site in search of evidence. (File)
WEST (May 14, 2013)--The State Fire Marshal's Office and the Bureau of Alcohol, Tobacco, Firearms and Explosives will announce the results Thursday of their weeks-long investigation of the deadly April 17 explosion at West Fertilizer Co.
A news conference is scheduled for late Thursday afternoon in West.
The announcement comes about a week later than originally expected.
Last week State Fire Marshal's Office spokeswoman Rachel Moreno said investigators had determined that ammonium nitrate stored at the plant is what exploded, but not what touched off the ammonium nitrate.
Moreno said a spot that is now a 90-foot-wide crater was where the ammonium nitrate was stored.
Investigators ruled out several possible causes of the initial fire at the plant that led to the explosion that killed 15, injured about 200, damaged or destroyed scores of homes and buildings including three of West's four schools and a nursing home.
"Weather, natural, anhydrous ammonium, the rail car containing ammonium nitrate, and a fire within the ammonium nitrate bin" all have been eliminated as possible causes, the Texas Department of Insurance said in a statement last week.
"Additionally, water used during firefighting activities did not contribute to the cause of the explosion," the department said.
"The investigation has revealed, to date, that the origin of the fire was in the fertilizer and seed building," the insurance department said.
Investigators are trying to pinpoint the exact location, the department said.
As many as 70 investigators were involved daily in the probe, the department said.
The blast site was painstakingly excavated from the outer edges to the epicenter in a search for evidence, officials said.
On Friday, the Department of Public Safety announced that DPS Director Steven McCraw had directed the Texas Rangers to join the McLennan County Sheriff’s Office in launching a criminal investigation of the blast.
"The citizens of McLennan County and Texas must have confidence that this incident has been looked at from every angle and professionally handled - they deserve nothing less," McLennan County Sheriff Parnell McNamara said in the statement issued by the DPS Friday.