The last five bombs allegedly made for a $15 million extortion scheme against an oil refinery were found after the FBI agreed to free a suspect's wife if he disclosed their location, an attorney said.

Gulf Oil Chemicals Co., which closed the Cedar Bayou plant Thursday after five bombs were found hidden inside the refinery, returned about one-third of the facility's 1,100 employees to work yesterday. One of the five bombs found in the plant exploded harmlessly while being defused, and the other four were safely deactivated, the FBI said.

Suspect John McBride last weekend disclosed the locations of the additional bombs in exchange for charges being dropped against his wife, Jill Renee Bird, Bird's attorney Robin Auld said. Auld said McBride passed a lie detector test given to determine the accuracy of his account of the plot.

Bird was released from jail shortly after a federal magistrate signed an agreement.

An extortion letter received Sept. 28 by Gulf officials was reported to have said that 10 bombs were hidden in the plant and that they would be detonated if the money were not received by last Sunday.

McBride, 46, and Bird, 34, were arrested Sunday in Durango, Colo. Theodore McKinney, 45, and Michael Worth, 34, were arrested in Apache Junction, Ariz., while on a telephone Friday night with a Gulf security official who was getting instructions on delivering the $15 million, the FBI said.