When any person indicted in the courts of this Commonwealth for a violation of its laws, has his case removed to the district court of the United States under 28 U.S.C. § 1442, it shall be the duty of the attorney for the Commonwealth for the county or city in which any such indictment is found to prosecute any such case in the United States district court to which the same shall be so removed, and for his services in this behalf he shall be paid a fee of $100 for each case tried by him in such United States district court, and mileage at the rate now allowed by law to the members of the General Assembly for all necessary travel in going to and returning from such court, to be paid on his account when approved by the Attorney General. A per diem of one dollar and fifty cents for each day of actual attendance upon such United States district court and mileage at a rate as provided by law for every mile of necessary travel in going to and returning from such court shall be paid out of the state treasury to each witness for the Commonwealth in every such case upon accounts therefor against the Commonwealth, certified by the attorney for the Commonwealth prosecuting such case and approved by the Attorney General. It shall not be the duty of the Attorney General to appear for the Commonwealth in such cases unless he can do so without interfering with the efficient discharge of the duties imposed upon him by law; but he may appear with the attorney for the Commonwealth prosecuting such case in any case when the interests of the Commonwealth may in his judgment require his presence. The Comptroller shall from time to time draw his warrants upon the state treasury in favor of the parties entitled to be paid the above compensation and expenses, or their assigns, upon bills certified and approved as above prescribed.