CAUSED THE EXPLOSION AND FIRE. INVESTIGATORS WERE ON THE SCENE TODAY - SIFTING THROUGH THE RUBBLE FOR CLUES. THE MARENGO POLICE SAY - THE HUGE PLANT EXPLOSION THERE LAST MONTH - THAT INJURED A DOZEN WORKERS - AND FORCED HUNDREDS PEOPLE OUT OF THEIR HOMES - WILL LIKELY BE RULED ACCIDENTAL. MARENGO POLICE CHIEF BEN GRAY - TOLD OUR NEWS-PARTNER KGAN-TV IN CEDAR RAPIDS - THAT THE IOWA DEPARTMENT OF NATURAL RESOURCES TRIED TO INSPECT THE FACILITY EARLIER THIS WEEK - BUT THEY WERE TURNED AWAY. THE PLANT'S OWNERS HAVE UNTIL MONDAY - TO PROVIDE THE DNR WITH AN LIST OF CHEMICALS AND SUBSTANCES THAT ARE IN THE BUILDING - AND ALSO PROVIDE A PLAN TO PROPERLY CLEAN-UP THE SITE. THE IOWA ATTORNEY GENERALS OFFICE IS SUING THE COMPANY - AFTER