Authorities have arrested a business associate of the woman who was killed in an explosion at a spa in California.
Stephen Beal, 59, was taken into custody on suspicion of possessing an unregistered destructive device and not in connection with Tuesday’s explosion, the FBI said.
An FBI spokeswoman said officials found the device while searching Mr Beal’s Long Beach residence.
Officials say they believe the blast “was not an accident”.
FBI spokeswoman Laura Eimiller said that no further details would be available until a federal criminal complaint was issued.
The victim, 48-year-old Ildiko Krajnyak, was the owner of the day spa in Aliso Viejo, where the blast occurred.
State documents show Mr Beal had listed Ms Krajnyak as the chief executive officer of a skin care company that he started last year called I&S Enterprises.
Mr Beal was the chief financial officer of the company, which was based in the building hit by the explosion.
Local media report that Mr Beal was also the ex-boyfriend of the victim.
His Facebook page contains several photos that appeared to show him travelling with Ms Krajnyak in the last year.
“We do not believe this was an accident,” FBI officer Paul Delacourt said on Wednesday.
“Although the damage was extensive, there are some components that we have located at the scene of the explosion that are inconsistent with what one might expect to find at this business.”
Mr Beal is expected to appear at the US District Court in Santa Ana on Thursday.
Tuesday’s blast, which witnesses described feeling like “an earthquake”, also left two people injured.
The explosion destroyed the first floor of the medical building where the spa was located and also damaged nearby buildings.