A grand jury investigation is underway to determine if government officials conspired against a former president. This probe is examining actions taken by officials over the past decade. An attorney for former CIA Director John Brennan disclosed that his client has been subpoenaed to testify.

The subpoena was presented to Brennan's attorney last Thursday. He is required to appear before a grand jury next month.

Further details about the investigation are available, including the specific focus of the probe and the individuals involved.