Each city of the first class shall contribute to the retirement system a sum equal to one hundred percent of the amounts deducted, in accordance with subsection (1) of section 16-1005, from each such police officer’s periodic salary. Such payment shall be contributed as provided in subsection (1) of section 16-1005 for employee contributions and shall be credited to the police officer’s employer account on a monthly basis. Each such account shall also be credited with regular interest. The city shall also contribute to the employer account of any police officer employed by the city on January 1, 1984, an amount equal to the employee contributions of such police officer that were made to the city prior to January 1, 1984, without interest, with such contribution to be made at the time the police officer retires or terminates employment with the city. The city may contribute such amount before the police officer’s retirement or termination of employment or credit interest on such contribution.