Casa Grande police and fire departments responded to the explosion, which occurred at 8 a.m. and left a door in the rear and portions of the building charred. No injuries were reported and the amount of damage has not been released.
The FBI was leading the investigation, which includes the Bureau of Alcohol, Tobacco, Firearms and Explosives and local law enforcement.
FBI spokesman Manuel Johnson said he could not confirm or deny an arrest was made, nor would he say if the agency was working any investigative leads.
“This thing is fluid,” Johnson said. “There are (other) agencies involved at this point and it would be really premature for me to start speculating.”
Johnson said the FBI would release a statement by the end of the day.
Patricia Raymond, a spokeswoman at Social Security Administration’s regional office in San Francisco, said the building was closed because it was before business hours. Typically, 14 employees work in the building.
Erin Bush, manager of the nearby Three G’s Flowers and Candle Store, said the explosion terrified her.
“I about fell out of my freaking chair,” she said. “I’m still shaking from it.”
Bush said she walked outside and saw smoke billowing from the building and firefighters from a nearby station running in the direction of the explosion.
“I have never in my life heard a boom like that,” she said. “It literally shook the windows.”
Richard Rose, a supervisor at a nearby Dairy Queen, said the boom was louder than anything he’s heard in action films in a movie theater.
“It was way louder than a car accident,” he said.
Rose said he saw officers from the nearby police station running toward the Social Security office.
Ed Mouradian was at the scene after the explosion. His wife, Faith, is an employee in the building and said he got a call from one of his wife’s co-workers about the explosion.
“She was crying and extremely upset,” Mouradian said. “I am concerned for all the employees’ well-beings. It’s a small office that’s very tight-knit.”