Investigator, yes. Special counsel, no. The scope of a special counsel investigation is suppose to be narrow. Any crime that a special counsel comes across that is not within the scope of his or her investigation must be passed along to the department of justice to be referred for investigation otherwise. This is the reason why Congress is demanding to know the original scope of the Mueller probe. Because Mueller is refusing to tell them.
Was the Kenneth Starr investigation narrow in scope? It was an investigation of a land deal in case you forgot.