The Justice Department has named former FBI Director Robert S. Mueller III as special counsel to investigate any ties between the Trump administration and Russia. How much authority does the special counsel have? What are the possible outcomes if the investigation uncovers evidence that ties do indeed exist?
The general powers of a special counsel are outlined under 28 CFR Part 600.
Section 600.5 outlines the powers and authority of a special counsel.
§ 600.6 Powers and authority.
Subject to the limitations in the following paragraphs, the Special Counsel shall exercise, within the scope of his or her jurisdiction, the full power and independent authority to exercise all investigative and prosecutorial functions of any United States Attorney. Except as provided in this part, the Special Counsel shall determine whether and to what extent to inform or consult with the Attorney General or others within the Department about the conduct of his or her duties and responsibilities.
A special counsel also has the authority to form his own staff as outlined under Section 600.5.
§ 600.5 Staff.
A Special Counsel may request the assignment of appropriate Department employees to assist the Special Counsel. The Department shall gather and provide the Special Counsel with the names and resumes of appropriate personnel available for detail. The Special Counsel may also request the detail of specific employees, and the office for which the designated employee works shall make reasonable efforts to accommodate the request. The Special Counsel shall assign the duties and supervise the work of such employees while they are assigned to the Special Counsel. If necessary, the Special Counsel may request that additional personnel be hired or assigned from outside the Department. All personnel in the Department shall cooperate to the fullest extent possible with the Special Counsel.
Basically, they have the same powers as a United States District Attorney. That will include the ability to conduct a thorough investigation of potential crimes committed and to issue subpoenas.
If the special counsel finds enough evidence, he can seek an indictment against the suspect from a federal grand jury. The grand jury will then decide whether to indict and the case would potentially go to a federal criminal trial.
However, it is unclear whether he can bring criminal charges against the President himself as Presidents usually cannot be criminally charged by normal prosecutors; the evidence should be presented to the House of Representatives as grounds for impeachment.