Speaking at a news conference on Wednesday, Orange County Sheriff's Department Undersheriff Don Barnes identified the victim as Ildiko Krajnyak-Vestil of Trabuco Canyon.
Three others were injured in the blast - two are expected to survive after surgery and a third was treated at the scene for smoke inhalation and released.
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FBI official Paul Delacourt said it appeared the explosion came from a device delivered to the location, though he did not know how the item was delivered. He said items that were possibly part of an explosive device have been sent to an FBI lab.
Three search warrants have been served in connection with the investigation - at the day spa business where the blast occurred, at a location in Long Beach and at another location in Trabuco Canyon, investigators said.
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FBI agents were seen removing boxes believed to contain evidence from a home along Dover Court in Trabcuo Canyon Wednesday morning. The home is believed to be Krajnyak-Vestil's residence.
Neighbors said Krajnyak-Vestil worked as an aesthetician at the medical office building on 11 Mareblu, where the blast occurred Tuesday. Barnes said she was likely the owner of the day spa there.
A neighbor who lives across the street from the Drover Court residence captured home surveillance footage of a man described by the neighbor as Krajnyak-Vestil's husband arriving home around 1 a.m. Wednesday. Two hours later, the footage shows several large, unmarked vehicles arriving and FBI agents getting out and approaching the home.
Area residents said the flurry of activity has come as a shock to them.Residents around the neighborhood also set up a GoFundMe account to help the family bring Krajnyak-Vestil's only son home from college and for the funeral.
If you want to donate, you may do so by going to gofundme.com/ildikokrajnyakmemorialfund.
No arrests have been made. Officials said other potential causes such as a gas leak have been ruled out.
Several businesses along Mareblu remained closed on Wednesday.
If you have any relevant information about this case, you're urged to contact authorities at 1-800-CALL-FBI.