Courts generally do not allow any public access to grand jury proceedings or documents. But federal rules and the majority of states, either expressly or impliedly, allow grand jury witnesses to disclose what transpired when they testified. In fact, President Clinton appeared on national television on the same day he testified before the grand jury and revealed his status as a witness.
But witnesses still may not enjoy complete freedom to talk publicly. A California Court of Appeal in Santa Clara in 2004 upheld a warning given to grand jury witnesses not to disclose their testimony, or anything they learned during their appearance before the grand jury, until the transcript is made public.
The case arose after a newspaper unsuccessfully tried to interview grand jury witnesses in connection with the criminal investigation of a local judge. The San Jose Mercury News complained that a witness declined to talk to one of its reporters after a prosecutor told the reporter, within earshot of the witness, that anyone who spoke publicly about his testimony could be thrown in jail. Another prospective witness refused to be interviewed without the district attorney's permission. The appeals court ruled that the admonition read to all witnesses was not an unconstitutional prior restraint on the press. (San Jose Mercury News, Inc. v. Criminal Grand Jury of Santa Clara County)
The ruling appears to conflict with a 1990 U.S. Supreme Court case, Butterworth v. Smith, which holds that all grand jury witnesses have a First Amendment right to disclose the contents of their testimony, at least once the grand jury has concluded its activities. But because the court in San Jose Mercury News limited its discussion to the single issue of prior restraint, it expressly declined to analyze the constitutionality of the warning under Butterworth.
One thing is certain: witnesses are completely free to discuss anything they knew prior to testifying before the grand jury. That doesn't mean they will be willing to do so, however -- especially when a prosecutor may threaten to throw them in jail for talking.
Grand jury "ancillary proceedings" -- court hearings on matters affecting a grand jury proceeding, such as motions to quash grand jury subpoenas, motions requesting immunity from prosecution and motions to compel testimony -- are also presumed to be secret. The press, in theory, can overcome the presumption by showing that the need for disclosure outweighs the need for secrecy. But case law indicates that such an argument has a slim chance of succeeding, especially if the grand jury's investigation is ongoing.
That is not to say the press can get no information at all about grand jury ancillary proceedings. Recently, Dow Jones & Co. petitioned the U.S. Court of Appeals in Washington, D.C., to release information that was redacted from the court's own opinion in the matter regarding subpoenas to New York Times reporter Judith Miller and Time reporter Matt Cooper. The court released the information regarding I. Lewis "Scooter" Libby, who had been indicted by then, but kept information related to other grand jury targets or witnesses confidential.