The retirement board shall be the trustee of the fund created by this chapter and shall have full power to invest and reinvest all funds to the extent the board deems appropriate, subject to the limitation that no investment shall be made except, on the exercise of bona fide discretion, in securities which at the time of making the investment are, by a statute, permitted for the investment of reserves of any domestic life insurance companies, provided the total sum invested in common and preferred stocks cannot exceed twenty per cent (20%) of the total of the fund. Subject to such limitations, the board shall have full power to hold, purchase, sell, assign, transfer, or dispose of any of the securities or investments in which the fund created herein have been invested, as well as of the proceeds of such investments and the moneys belonging to the fund.

The state treasurer shall be the custodian of the fund. All payments from the fund shall be authorized by the state treasurer on vouchers duly issued by the state treasurer.