A deadly explosion at an office building in Southern California Tuesday is being investigated as a crime and is believed to have been triggered by a package, though no physical proof has been found on scene, federal officials said during a press conference Wednesday afternoon.

"At this time we have ruled out the potential of this to be an accident due to the condition of the victim," an official with the Orange County Sheriff's Department told reporters. "Evidence collected and what we believe are involved in the explosion are not consistent with items that would be used at a day spa."

"Investigators are still working to confirm whether or not this was an intentional act. We are, however, investigating this as a crime," the official added.

One person was killed and three others wounded as the result of an explosion inside a two-story building in Aliso Viejo, about an hour's drive south from Los Angeles. Ildiko Krajnyak was identified as the woman killed in the blast, and she owned a day spa on the first floor of the building.

A portion of the building's walls were blown off, and witnesses said it felt like an earthquake hit during the blast.

First responders and federal officials still have not found an explosive device they believe would have triggered the explosion.

Officials served three search warrants Wednesday, including to a business in the affected building; one in Long Beach, Calif.; and another in Trabuco Canyon, Calif. No arrests have been made.

Federal officials were asked if there are other targets and said they won't "rule out anything."

The FBI, ATF, and Orange County Sheriff's Department's bomb technicians remain on scene investigating the incident.

The explosion comes two months after the Austin, Texas, bombings. From March 2-20, five package bombs exploded at different places throughout the city, killing two and injuring five.

The suspect committed suicide during a police encounter March 21.