WEST, Texas — A state fire official says there’s no sign of criminal activity in the explosion of a fertilizer plant in Central Texas that killed 14.

Assistant State Fire Marshal Kelly Kistner said Saturday that authorities will begin removing four tanks from the plant in West as a precaution to safeguard those working there. Kistner said the tanks contain ammonium nitrate and anhydrous ammonia.

He said investigators still do not know where on the property the fire began.

A fire touched off a massive explosion Wednesday at the West Fertilizer Co., destroying homes, schools and a nursing home within a several-block area of the site.

Kistner said no other materials on the site pose any danger.

Robert Champion, the special agent in charge for the Dallas office of the federal Bureau of Alcohol, Tobacco and Firearms, said experts plan to enter the crater in the next few days and start digging in search of an explanation.

“It’s a slow process, but we’re getting there,” Champion said.

Nearly 70 federal and state investigators are still trying to determine what caused the fire that set off the explosion, Kirstner said.