N.J. Stat. § 43:13-16: Deposit and investment of fund; income

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