The blast at an Aliso Viejo, Calif.-based office complex, which housed several medical offices, occurred at a day spa located on the building's first floor when the business owner opened a cardboard box, CNN reports.
Investigators found a nine-volt battery, a cellphone and loose wires among the debris, in addition to melted duct tape.
The May 15 explosion killed the day spa's owner, Ildiko Krajnyak, and injured three others. Court documents show one of the victims said the box exploded as soon as Ms. Krajnyak opened it.
After an investigation of Ms. Krajnyak's business partner and ex-boyfriend's home, Stephen Beal, was charged with one count of possession of an unregistered destructive device — a charge that is not in connection with the spa explosion. He remains in police custody until a detention hearing May 21.
Mr. Beal claims the items investigators found in his home — which include "precursor chemicals, energetic materials, e-matches, variously sized cardboard and modified rocket tubes" — were used to build model rockets. Ms. Krajnyak and Mr. Beal ended their relationship in February or March 2018, but remained business partners
One day after the explosion, authorities said they believed the incident was intentional. "At this point, our working theory is that this explosion was caused by a device," said Paul Delacourt, assistant director in charge of the FBI's Los Angeles field office, according to CNN. Police have not discussed a motive, but an FBI spokesperson said they have ruled out terrorism.
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