The disability and relief fund for firemen and policemen shall be a special trust fund and shall be disbursed only in the manner hereafter provided. Such fund shall be a part of the public funds of the Public Employees’ Retirement System and shall be kept by the board as it is required to keep its other funds. Interest earned on said fund shall be credited to and become a part of said fund. All moneys on deposit in such funds on July 1, 1987, shall be paid over to the Board of Trustees of Public Employees’ Retirement System on or before July 1, 1987.