The grand jury shall investigate and report on the operations, accounts, and records of the officers, departments, or functions of the county including those operations, accounts, and records of any special legislative district or other district in the county created pursuant to state law for which the officers of the county are serving in their ex officio capacity as officers of the districts. The investigations may be conducted on some selective basis each year, but the grand jury shall not duplicate any examination of financial statements which has been performed by or for the board of supervisors pursuant to Section 25250 of the Government Code; this provision shall not be construed to limit the power of the grand jury to investigate and report on the operations, accounts, and records of the officers, departments, or functions of the county. The grand jury may enter into a joint contract with the board of supervisors to employ the services of an expert as provided for in Section 926.