A civilian engineer from Virginia who worked for the Naval Sea Systems Command and his 80-year-old father were indicted on Thursday in Rhode Island in an alleged bribery and fraud plot that prosecutors say cost the U.S. Navy about $10 million over 15 years.

The indictment of Ralph M. Mariano, 54, of South Arlington, Va., and his father, Ralph Mariano Jr., of North Providence, R.I., came after three others accused in the plot pleaded guilty to charges and agreed to cooperate with federal authorities.

Prosecutors allege that Ralph Mariano used his authority at the Naval Undersea Warfare Center in Newport, R.I., and his oversight of certain Navy contracts to arrange for naval funds to be funneled back to him directly, and through other companies beginning in 1996 and continuing until January 2011.