FRANKFORT, Ky. (AP) -- Federal prosecutors say in a court filing that a former Transportation Cabinet official who is a cooperating witness secretly recorded conversations with then-Transportation Secretary Bill Nighbert before an investgation into highway bid-rigging began.

Jim Rummage has been identified in the case against Nighbert and contractor Leonard Lawson as someone who secretly recorded calls with Lawson and others at the direction of the FBI.

Prosecutors allege that Rummage and Nighbert were conspiring to leak confidential estimates to Lawson.

Rummage has not been charged. Lawson and Nighbert have pleaded not guilty in the case. They are also charged with obstructing justice along with Lawson company employee Brian Billings, who also pleaded not guilty.

Defense lawyers have argued against admitting tapes during trial and have sought a hearing.