The State Treasurer shall be the custodian of the funds and securities of the retirement system and may deposit the funds and securities in any financial institution approved by the Nebraska Investment Council. The Director of Administrative Services is directed to draw warrants on the State Treasurer against the fund for authorized expenditures upon duly itemized vouchers signed by a person authorized by the retirement board. The State Treasurer shall transmit monthly to the board a detailed statement showing all credits to and disbursements from the funds in his or her custody belonging to the retirement system.