(5 ILCS 305/1) (from Ch. 111, par. 2701)
    Sec. 1. No State, county or municipal officer, whose duty it is to investigate the commission of any crime or to prosecute persons accused of crime, shall employ any detective or investigator on a compensation basis other than that of time, and in no event shall compensation to such persons be contingent on the success of the investigation or prosecution. Evidence obtained in violation of this act shall be inadmissible in any court in this State for any purpose and any person employed in violation of this act shall be incompetent to testify in any such court as to any information or evidence acquired by him in such employment.
(Source: Laws 1929, p. 347.)