The Attorney General and the agents appointed by him, when authorized so to do by the Attorney General, may expend such sums as the Attorney General deems necessary in the purchase of controlled substances for evidence and in the employment of operators to obtain evidence.

The sums so expended shall be repaid to the officer making the expenditures upon claims approved by the Attorney General and subject to postaudit by the Department of Finance. The claims when approved shall be paid out of the funds appropriated or made available by law for the support or use of the Department of Justice.