A complaint against any officer or employee of either department may be orally or in writing lodged with the commission or any member thereof. The commission or any member may investigate the charge, and if a prima facie case is found to exist, the officer or employee may be brought to trial by the commission. But the commission, five days before any such trial, shall have served upon the officer or employee a written statement of the charges upon which the trial is to be had. In or for the conduct of such trial, the commissioners shall have the power to secure by summons both the attendance and testimony of witnesses and the production of books and papers relevant to such trial. And the accused shall have the same right. At any such trial both the commission and the accused may be heard in person or by counsel, and the city council may employ counsel to prosecute the case and fix the fee to be paid for such services.