The Tuesday afternoon blast shattered windows and forced children in a nearby daycare center to be evacuated.
No children were hurt.
The working theory is that the explosion was from a device, the Federal Bureau of Investigation said. White asked for privacy as they mourn her. The neighbor says Krajnyak was her mother's caretaker and describes the husband as a massage therapist and nice man.
He said buildings in the area had been damaged by the blast. Police have tentatively identified the dead woman as Ildiko Krajnyak of Trabuco Canyon, California, who is believed to be the owner of the day spa, he added.
Her Orange County business offered services such as facials, waxing and wrinkle treatments.
The house in Trabuco Canyon was owned by Krajnyak and her estranged husband, and the couple were facing foreclosure. Barnes initially said she was 40 years old; the sheriff's office later said that she was 48.
Associated Press writer Michael Balsamo in Los Angeles contributed to this report.
Investigators believe an explosion at a medical office in southern California that killed one woman may have been intentional, USA media reports say. But the sheriff's department tweeted late that evening that it has not "conclusively identified the source of the explosion" and the "investigation is in early stages".
"At this point, we do not believe this was an accident".
The two customers injured underwent surgery Wednesday and were expected to survive.
A United States official told the Associated Press the authorities were investigating it as an intentional act and a package may have caused the blast. The powerful blast injured three people and caused the ground to shake in nearby structures. Officials said other potential causes such as a gas leak have been ruled out.
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No arrests have been made.
The Orange County hazmat team, bomb squad, FBI, and Department of Homeland Security, investigate the scene of an explosion in Aliso Viejo on Tuesday, May 15, 2018.
Officials are investigating an explosion that killed a woman and injured three other people at a Southern California medical office building.
All businesses on Mareblu are closed Wednesday and the street is closed to traffic while the law enforcement investigation continues, according to the City of Aliso Viejo.
Evidence has been sent back to the FBI's lab in Quantico, Virginia, for testing.
The Tuesday afternoon blast occurred in Aliso Viejo, which is about 50 miles south of Los Angeles.
A federal official told The Associated Press late Tuesday that the explosion is believed to have been intentional and may have come from a package.
Fennessy says the blast involved a building under renovation.
Shin said it felt like "a big natural disaster", and as he and others rushed downstairs to get out of the nearby building, he saw two holes in the wall of the medical facility. A third victim was treated for smoke inhalation.
There's no word yet on a motive for the explosion.