A U.S. Attorney can prosecute anyone if they find criminal activity, not just current or former govt employees.
>Statement of Policy: This policy establishes guidelines for the exercise of discretion by appropriate officers of the Department of Justice in determining whether to bring a federal prosecution based on substantially the same act(s) or transactions involved in a prior state or federal proceeding. See Rinaldi v. United States, 434 U.S. 22, 27, (1977); Petite v. United States, 361 U.S. 529 (1960).
https: //www.justice.gov/usam/usam-9-2000-authority-us-attorney-criminal-division-mattersprior-approvals#9-2.030
US Attorneys prosecute federal crimes against anyone, civilian or govt employee.