ALISO VIEJO, Calif. (AP) -- A U.S. official says a deadly explosion at a Southern California office building is being investigated as an intentional act and investigators believe the blast may have come from a package.
One woman was killed and three others were injured during the Tuesday afternoon explosion at a medical office building in Aliso Viejo.
The official said the information was based on a preliminary investigation. Investigators said they hadn't yet located an explosive device and were searching through debris.
The official was briefed on the investigation but wasn't authorized to discuss the matter publicly and spoke to The Associated Press on condition of anonymity.
Agents from the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives were at the scene Tuesday night.
Sheriff's officials said the size of blast made it suspicious.