N.J. Stat. Ann. § 43:7-20

Said pension commission shall deposit such fund in any of the banks or trust companies of the State, and shall invest the same in bonds secured by first mortgages on improved property worth at least twice the amount loaned, or in bonds of the United States or of this State, or any city or county in this State. All income, interest or dividend which shall be paid or agreed to be paid on account of any loan or deposit shall belong to and constitute a part of said fund.