Officials have determined that ammonium nitrate stored at a Texas fertilizer plant is what exploded on April 17, killing 14 people and injuring hundreds.
The finding was expected, and officials had said they were focusing their investigation on the explosive chemical used in many fertilizers.
But State Fire Marshal's Office spokeswoman Rachel Moreno says it's still undetermined what touched off the ammonium nitrate.
She said findings on what caused the blast on the outskirts of the small town of West will be delayed. They had been expected Friday.
Moreno said a spot that is now a 90-foot-wide crater was where the ammonium nitrate was stored.
Also, federal emergency officials have begun offering shelter for West residents whose homes were destroyed or severely damaged. About 70 homes were damaged or destroyed.