The moneys received by the association must be kept in a trust fund known as the association state fund. The assets of the fund must be held in trust. No part of the assets of the fund may be used for or diverted to purposes other than for the exclusive benefit of the members, their spouses, or the members’ beneficiaries prior to the satisfaction of all liabilities of the fund with respect to them, provided that the fund may be used to pay reasonable administration expenses of the association. The moneys received from the state, city, or employee’s salary contribution must be deposited in the association state fund and may be expended only for the purposes set forth in section 18-11-14. The relief association shall manage and control all moneys that come into its possession. Moneys in the fund may be invested in bonds of the United States, bonds of the state of North Dakota or any other state, in certificates of indebtedness of the state of North Dakota, in any bonds or certificates of indebtedness of any political subdivision of the state of North Dakota which constitute the general obligations of the issuing tax authority, or the Bank of North Dakota or any other bank or savings and loan association which is insured by the United States. The board may also invest all or part of the moneys in the fund in other investments by selecting a funding agent or agents and establish an investment agreement contract. The contract must authorize the funding agent or agents to hold and invest those moneys for the board. The moneys invested must be placed for investment only with a firm or firms whose primary endeavor is money management and only after a trust agreement or contract has been executed.