if you believe that the contractors may have over-billed for work or nonwork, then you will need to prove it.  each contract has a contract administrator that manages the contract for hart, to ensure that all work is done according to the terms of the contract and that all bills and payments are valid.  to have corruption is such a setting there must be collusion between hart personnel and the contractor.  further proof will have to be made of illegal payment made between contractor personnel and hart personnel, such payments are made outside of the contract.  you will need to audit the contractor's books to see if there were any illegal payments received or paid and audit the employee of hart receiving the bribe (his/her personal finances).  there are 8 years of contractor work, are you going to audit all 8 years?  this would be time consuming and costly.  you will need not only to audit hart, but the contractor and hart's employees who may have been involved.  not easy.