Officials probe disappearance of 30 tons of explosive chemicals during rail shipment.

A 30-ton shipment of ammonium nitrate, a chemical used to make both fertilizer and explosives, disappeared from a railcar en route from Wyoming to California. The chemical's supplier, Dyno Nobel, said it thought the shipment, which was in pellet form, fell from the railcar. Officials are investigating the disappearance, but do not believe there is any criminal or malicious activity involved. Ammonium nitrate was the primary explosive used in the 1995 Oklahoma City bombing that killed 168 people.