At the end of the fiscal year, the board of trustees may invest any surplus left in the police pension fund, but no part of the moneys realized from any tax levy shall be used for any purpose other than the payment of pensions. Such surplus funds may be invested in interest-bearing bonds of the United States or the state of North Dakota, or bonds or warrants of any county, township, or municipal corporation of this state which constitute the general obligations or contingent general obligations of the issuing tax authority, or investments with any federally insured bank or savings and loan association. All securities shall be deposited with the treasurer of the board for safekeeping. The board may also invest all or part of such surplus funds in other investments by selecting a funding agent or agents and establish an investment agreement contract regarding such surplus funds. The contract shall authorize the funding agent or agents to hold and invest such funds for the board and such funds shall 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. The board of trustees may pay the fees and charges of said funding agent or agents from any surplus remaining in the police pension fund in excess of the moneys realized from any tax levy. The board of trustees may use a portion of the surplus left in the police pension fund in excess of moneys realized from any tax levy to pay the cost of actuarial studies of said pension system.