Something else I found, in an article about this particular case, which has probably been covered here but is interesting to repeat:
Anyone who's subpoenaed in the inquiry, noted the lawyer, can be almost certain that prosecutors aren't contemplating indicting him or her. Subpoenas are rarely sent to the targets of an investigation, and if they are, the recipients must be told in advance that they are considered targetsat which point they would almost certainly cite the 5th Amendment and refuse to answer questions. Link
so then if Judith Miller was a target??