When the State's Attorney of a county, on the order of a Superior judge or the Attorney General, for use in a criminal cause pending in his or her office, requests an expert investigation, chemical or pathological, of a substance, such investigation shall be made at the laboratory forthwith, without charge to the State; and the expert making or interpreting such investigation shall submit the results of such expert's work to such State's Attorney, and shall attend court as a witness at any place in the State when required to do so by subpoena, and submit in court the results of such expert's investigation; and he or she shall be paid as such witness his or her actual expenses of attendance when summoned by the State. (Amended 1985, No. 267 (Adj. Sess.), § 16.)