The Sixth Man by David Baldacci

The Sixth Man - Sean King and Michelle Maxwell are engaged to help attorney Ted Bergin to defend Edgar Roy, an accused serial killer now residing in a federal facility for the criminal insane.  On their way to meet with Bergin, King and Maxwell find Bergin's body in his car along the road.  Because Bergin was Roy’s attorney, the FBI becomes involved in the investigation.  King and Maxwell find themselves the target of unknown assailants also.  What they don’t know is that Roy was involved in a Federal intelligence unit known as the E-program that members of the intelligence community want destroyed because it usurps their power.