My federal grand jury summons told me that, if the Court selected me to serve, I would serve “twice a week for 18 months.” I served, and I learned more about the mechanics of grand juries than my Stanford Law degree could have taught me.
Now that Special Prosecutor Robert Mueller has opened a case in a federal grand jury in the United States District Court for the District of Columbia, these mechanics may help explain what weight to put on Mueller’s action.
I. The Court conscripted me.
I never shied from my duty or sought to avoid it, but I marveled at the power of the United States to conscript citizens. On the first day of my new job at the United States Department of Justice in 2008, I told my Section Chief that the United States District Court for the District of Columbia had summoned me for the grand jury pool.
I did not expect the Court to select me because I was serving as a Trial Attorney in the Department of Justice, and some of the prosecutors serve as Trial Attorneys in the Department of Justice. Nonetheless, I soon joined a pool of hundreds of citizens in the Ceremonial Courtroom in the District Court for the District of Columbia. From that pool, the Court would choose twenty-three grand jury members.
II. Chief Judge Lamberth asked whether I could serve on a grand jury and at the Department of Justice.
The clerks explained the selection process. After summoning others to a back room, eventually, they brought me back to meet Chief Justice Royce C. Lamberth. He asked me several questions.
“In what Department of Justice section are you serving?” “The Natural Resources Section of the Environment and Natural Resources Division.”
“Have you ever done criminal work for the Department of Justice?” “No.”
And then I knew the Chief Judge would likely empanel me on the jury. “Can you fairly assess the evidence and come to unbiased, reasonable results based on that evidence?” I believed that my experiences and my training had only helped me refine my objectivity. “Yes.”
That day, I took another oath to uphold the United States Constitution and laws of the United States. The Court empaneled me on U.S. Grand Jury 08-1 for the District of Columbia, and I served as the Docket Clerk, or secretary, for two years.
Federal Rule of Criminal Procedure 6(e) generally compels grand jurors to keep secret everything they learn. It permits only very narrow exceptions. Nonetheless, I saw first-hand the mechanics of grand jury operations.
III. Federal prosecutors can file criminal charges in court only after demonstrating probable cause to a grand jury.
Make no mistake: the prosecutor, and not the grand jury, drives the investigation. Grand juries solely assess the evidence the prosecutors develop to determine whether the prosecutors have demonstrated probable cause.
The Fifth Amendment prohibits federal prosecutors from charging anyone for any “capital, or otherwise infamous crime” unless a grand jury indicts that target. Therefore, prosecutors seek to demonstrate probable cause to a grand jury, so the grand jury will indict a target. Prosecutors demonstrate probable cause if they show someone probably committed a crime and the target probably committed that crime.
IV. Prosecutors open cases in grand juries to obtain subpoena power.
Federal prosecutors open cases to obtain power to subpoena documents on behalf of a grand jury. Grand juries hold subpoena power, but they do not exercise it directly. After opening a case, the Department of Justice U.S. Attorney’s Manual lets prosecutors subpoena individuals to produce documents or to testify before the grand jury.
If a prosecutor issues a subpoena and the target declines to produce the documents or declines to testify, the prosecutor can move to compel in court, and the judge can encourage the document-producer or witness to comply. A court can jail someone for failing to do so. Under this method, prosecutors jail reporters at times.
V. Prosecutors drive the investigations.
After opening a case, the prosecutors review the documents, interview witnesses, and pursue the investigation without consulting the grand jury further. Because the Department of Justice’s culture compels it to treat grand jury time as scarce and valuable, prosecutors often subpoena witnesses only if the witnesses do not cooperate voluntarily.
When the prosecutor believes it has evidence sufficient to qualify as probable cause for the crimes it seeks to pursue in court, it asks the grand jury to deliberate and to decide whether to indict the target. Sometimes, the law enforcement agent testifies about what he or she learned from the documents and witness interviews. In contrast to trial juries, nothing stops grand juries from considering hearsay evidence. If the grand jury declines to indict a target, prosecutors decide whether to supplement their existing evidence to satisfy the grand jury or whether to drop the case.
Thus, grand juries have no authority to initiate any investigation, to stop any investigation, or to guide any investigation. When anyone describes a grand jury doing anything except indicting someone, that person misunderstands the grand jury’s limited power.
VI. Mueller had no reason to empanel a new grand jury.
Reports conflict on whether Mueller “empaneled a grand jury” or whether he just opened a case in front of grand jury. Likely, he just opened a case, so he could subpoena documents and, if necessary, witnesses.
As a special prosecutor, Mueller exercises “the full power and independent authority to exercise all investigative and prosecutorial functions of any United States Attorney.” Therefore, he had the same access to the existing grand juries as other Department of Justice prosecutors.
The District of Columbia grand juries have the capacity to review Mueller’s investigation. When I served from 2008 to 2010, the District of Columbia had four grand juries to which prosecutors could present evidence. Two assessed the evidence in guns-and-drugs cases, and two assessed the evidence in other, often more complicated, crimes. We did not serve all day, every Wednesday and Friday, but between two and seven hours most of those days.
Therefore, Mueller had no reason or need to empanel a special grand jury. The grand juries in Washington, D.C., already gave him the tools he needed to subpoena documents and witnesses, to interview witnesses, and to indict anyone.
 Fed. R. Crim. P. 6(g) (“A grand jury . . . may serve more than 18 months only if the court, having determined that an extension is in the public interest, extends the grand jury’s service . . . [by] 6 months . . . .”).
 Sean Illing, How important is it that Mueller has formed a grand jury? I asked 20 legal experts, Vox (Aug. 4, 2017), at https://www.vox.com/2017/8/4/16092128/robert-mueller-donald-trump-russia-grand-jury.
 I left my position in February 2017. This blog post expresses my views and do not necessarily reflect the views of the United States or the United States Department of Justice.
 Fed. R. Crim. P. 6(a)(1).
 Beavers v. Henkel, 194 U.S. 73, 84 (1904) (“The grand jury is a body known to the common law, to which is committed the duty of inquiring whether there be probable cause to believe the defendant guilty of the offense charged.”).
 U.S. Const., Fifth Am. (“No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury . . . .”).
 See Stewart v. Abraham, 275 F.3d 220, 228 (3rd Cir. 2000) (recognizing that Pennsylvania required the prosecutor to show probable cause before holding a defendant: “at least a prima facie case that a crime has been committed and that the accused is probably the one who committed it.”); Nix v. Sweeney, 573 F.2d 998, 1001 (8th Cir. 1978) (explaining that probable cause for arrest requires the officer to believe, first, “that a crime has been committed, and, second, that the accused more probably than not participated in it.”).
 See U.S. Attorney Man. § 9-11.140 (recognizing that prosecutors can issue subpoenas only for “grand jury proceedings”), available at https://www.justice.gov/usam/usam-9-11000-grand-jury.
 Shillitani v. United States, 384 U.S. 364, 370-71 (1966) (“There can be no question that courts have inherent power to enforce compliance with their lawful orders through civil contempt. And it is essential that courts be able to compel the appearance and testimony of witnesses. A grand jury subpoena must command the same respect. Where contempt consists of a refusal to obey a court order to testify at any stage in judicial proceedings, the witness may be confined until compliance.”).
 See, e.g., Branzburg v. Hayes, 408 U.S. 665 (1972).
 Fed. R. Evid. 1101(d), (d)(2) (“These rules [of evidence]—except for those on privilege—do not apply to . . . grand-jury proceedings.”).
 28 C.F.R. § 600.6.
[Updated on November 18 to clarify one sentence and otherwise to fix some typos.]