ORANGE, Calif. >> A California man was arrested in a spa explosion that killed his ex-girlfriend last year after authorities painstakingly analyzed remnants of a bomb they traced to the suspect, his home and car, federal prosecutors said today.

Stephen Beal, 59, had been arrested shortly after the bombing last year for investigation of possessing explosives, but was freed when prosecutors questioned whether material found at his home met the legal definition of a “destructive device.” Now, after further testing of evidence, Beal is being held on a charge of malicious destruction of a building that included a death, a charge that could carry a life sentence.

Ildiko Krajnyak, 48, was killed and two female clients were severely wounded May 15 when she opened a box that erupted in a fiery explosion at the spa in the city of Aliso Viejo, about 50 miles south of Los Angeles, investigators said.

“This was a horrific intentional attack that killed an innocent woman and severely injured two others,” U.S. Attorney Nick Hanna said at a news conference in Orange, California.

Krajnyak had told friends she was afraid of Beal after he made threats following their breakup. Beal told investigators he felt betrayed when she told him she was in a relationship with another man, Hanna said.

Authorities suspect Beal, a partner in the salon, delivered the bomb to the business while Krajnyak was visiting family in Hungary.

Krajnyak had returned from that trip and had just finished treating a mother and daughter, who were at the front desk when she picked up one of three or four cardboard boxes and opened it.

The blast knocked the two customers off their feet and the older woman told police it lit “everything on fire.”

First responders thought they were dealing with a car bombing or gas main rupture, said Paul Delacourt, the FBI’s assistant director in charge of the Los Angeles office.

The explosion blew out a big hunk of the building and body parts were found in the parking lot.

Beal — a model rocket hobbyist — was arrested at the time and released when prosecutors dropped a charge against him. Over nine months, investigators were able to make the case by piecing together fragments from the bomb that they could connect to Beal, including a battery, a wire and boxes similar to the one that delivered the fatal blow.

“While the victim had expressed fears about Mr. Beal and he possessed material that could be used to manufacture a bomb, it was forensic evidence collected at the scene, analyzed and pieced together into a coherent whole that allowed us to file this case,” Hanna said.

Delacourt detailed how investigators and personnel at the agency’s Quantico, Virginia, lab were able to connect Beal to internal components of a battery found 10 days after the blast.

The battery part was traced to a specific shipment that arrived in the U.S. from China and ended up in a store near Beal’s home. Video showed Beal paying cash for that type of battery. Investigators were able to eliminate others who bought those batteries from suspicion.

“This was the exhaustiveness of the effort,” Delacourt said.

Beal’s lawyer declined to comment.

Beal had denied making bombs and said he did not have material for an explosion as powerful as the one he saw in news coverage, according to court records from last year.

At the time, investigators said they found two improvised explosive devices, three firearms and more than 100 pounds of explosive material during a search that Beal allowed of his house.

Steve Young, a friend and neighbor, said he does not think Beal is capable of harming anyone.

“I don’t feel that he’s the type of person that would do this sort of thing,” he said

Beal and Krajnyak split up, but remained business partners at the spa where she was a licensed cosmetologist.

An affidavit in support of the arrest said during a voluntary interview Beal said the romance “cooled” in early 2018.

“Beal stated he took a trip with Krajnyak to Portugal during which Krajnyak admitted to Beal that she was in an intimate relationship with another man from Northern California,” the affidavit said “Beal stated he was hurt and betrayed when Krajnyak told him this.”