LOS ANGELES (AP) -- Federal and local investigators searched through debris, looking for remnants of a possible explosive device, after a blast at a Southern California medical office building that left a woman dead and three other people injured.
The explosion occurred around 1 p.m. Tuesday in Aliso Viejo, about 50 miles (80.5 kilometers) south of Los Angeles. It blew siding off the walls, exposing insulation and framing and shattering windows at the two-story building that houses medical offices.
"The corner of that building, the whole bottom floor is pretty much blown out," fire Capt. Tony Bommarito said.
The cause of the blast remained a mystery for much of the day, with officials initially believing a car had smashed into the building. But sheriff's officials said the size of the blast made it suspicious.
A federal official told The Associated Press late Tuesday that the explosion was believed to be an intentional act and the blast may have come from a package.
The official said the information was based on a preliminary investigation. Authorities said they hadn't yet located an explosive device and were searching through debris.
The official, who was briefed on the investigation, was not authorized to discuss the matter publicly and spoke to The Associated Press on condition of anonymity.
Bomb technicians and agents from the Orange County Sheriff's Department, the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives were at the scene Tuesday night.
"We have not found any type of specific device inside of the building right now that would tell us or lead us to exactly what the device was, if there was a device," sheriff's Cmdr. Dave Sawyer said.
The woman who was killed inside the building was "in close proximity" to the explosion, Sawyer said. The three people who were injured were nearby and were being questioned by investigators late Tuesday night, he said.
"Anytime you see an explosion of this magnitude, it would definitely be suspicious to us," Sawyer said.
Authorities were not searching for any specific suspects Tuesday night, but the investigation was continuing, he said.
Mary McWilliams told the Orange County Register that she arrived for an appointment to find smoke surrounding the area and car alarms going off.
McWilliams said she saw two burned women staggering out of the building, covered in ash and soot.
One woman, who had skin peeling on her arm from burns, said, "Take care of my mother," McWilliams said. The other woman was bleeding from her head.
Fire officials said a third person suffered smoke inhalation.
A daycare center and preschool across the street was evacuated. Some children held hands as they were led out by firefighters while sheriff's deputies rolled out babies in cribs.
"When I was playing outside I heard the big crash, I thought it was a garbage truck but it was a building that smashed," 6-year-old Kingston Dik told KNBC-TV.
No children were hurt.