Moneys contained in the Indigent Offender Trust Fund shall be expended by the Commissioner of Mental Health for purposes set out in Section 12-23-15. Such moneys shall be used and expended by the Commissioner of Mental Health to establish, organize, and administer the indigent offender alcohol and drug treatment program throughout the state, including all functions or projects of the Department of Mental Health directly or indirectly relating thereto. Any unexpended or unencumbered sums remaining in the fund at the end of the fiscal year except appropriations from other state funds shall remain in the fund to be preserved for the administration of the indigent offender treatment program.