Generally, in white-collar crime situations, particularly antitrust, the first time a client may know he is under investigation is after the grand jury proceedings have commenced. The client will usually find out about the investigation through the industry grapevine, through the receipt of a subpoena by his employer or through a subpoena ad testificandum to an individual in his company. It is necessary for an attorney to understand the investigative process in order to properly represent his client in the antitrust proceedings that follow.
Carl L. Steinhouse,
A Practical Approach to Representation of a Client during a Federal Antitrust Grand Jury Investigation,
29 Clev. St. L. Rev.
available at https://engagedscholarship.csuohio.edu/clevstlrev/vol29/iss1/23