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.”