The sprawling investigation into Russia meddling in the 2016 election has reportedly broadened to include potential financial crimes and obstruction of justice. But the probe now being led by special counsel Robert Mueller originally began as a counterintelligence investigation, which means a grand jury may have to contend with classified evidence obtained through highly sensitive surveillance and counterespionage tactics.

American intelligence allegedly captured the Russian ambassador’s account of a purported meeting at the Mayflower hotel with then-Sen. Jeff Sessions, fired national security adviser Michael Flynn’s controversial phone call with that same ambassador during the Trump transition, and contacts between Russian interests and people associated with the Trump campaign, according to various reports over the past several months.

It’s not yet clear which, if any, of these incidents will make their way to a grand jury—which Mueller has reportedly begun using—but the Justice Department has well-established protocols for how to balance keeping top state secrets under wraps while getting the right information in front of a grand jury, according to legal experts.

Grand juries already operate under an extraordinary level of secrecy. Neither the jurors, nor the prosecutors, nor the court staffers involved in their meetings, are allowed to transmit to the outer world what’s going on behind their closed doors. Only the witnesses called to testify, and their lawyers, can discuss publicly their involvement.

A grand jury overseeing an investigation that potentially involves classified information is subject to an additional layer of protocols constraining if and how those relevant disclosures are put in front of the jurors.

“Yes, classified information is presented to the grand jury,” Rebecca Lonergan, a former federal prosecutor who handled foreign surveillance cases, told TPM. “But it’s often presented in a format that the government is, as much as possible, protecting the most sensitive aspects of its classified materials.”

The U.S. Attorney’s Manual, which offers across-the-board DOJ operating policy, lays out the protocol: prosecutors cannot discuss classified information with witnesses who don’t have the proper clearances, and grand jurors can’t hear or read classified information unless the relevant intelligence agency okays it.

“These are average citizens who are coming in off the street, so they don’t have security clearances. And the prosectors will not be able to even use that type of information unless they’ve gotten the permission of whichever arm of the government is in control of the information,” said Lori Shaw, a criminal law professor at the University of Dayton and an expert on federal grand juries.

To facilitate that approval, according to the handbook, the prosector can use an “unclassified summary of the information prepared by the prosecutor in concert with the [intelligence community] agency” or the agency can “declassify the particular document(s) involved, in whole or in part, by excising certain portions that make the document particularly sensitive but that are not relevant to the use desired by the prosecutor.”

In practice, prosecutors on cases that involve sensitive information are working with the relevant intelligence agencies from step one, so they know what information they will be able to use with a grand jury, as well as during the trial phase, which will be much more transparent.

“There are protocols and relationships that are established with liaisons at each of the intel community agencies to work with Justice officials, including Mueller,” said Randall Samborn, who served as a spokesperson for Patrick Fitzgerald, the special counsel in the Valerie Plame leak investigation.

Grand juries operate under a lower evidentiary threshold than a trial court, and the evidence is subject to laxer rules. This gives the prosecutor more flexibility in presenting to the grand jury only portions of information related to the charges he or she is contemplating. Prosecutors will also be considering which pieces of classified evidence they may need for trial–and weighing what they will eventually have to turn over to defense counsel. By working with the intel agencies early on, prosecutors will know whether they’ll have issues bringing certain pieces of evidence into the trial phase, which will be more public and there will be battles with the defense side over what evidence gets submitted.

“It would be totally acceptable for grand jurors to act upon information that has been summarized or redacted that makes the same underlying points to their satisfaction of the substance of the classified marital,” Samborn said.

According to Lonergan, who now teaches at USC Gould School of Law, summary witnesses are a very common tool for prosecutors to relay the vital points underlying classified information without giving up state secrets surrounding it.

“What you present to the grand jury is also going to be, in a sense, redacted before you present it, because most of what you present to a grand is not going to be in reports or things like that,” she said. “The way that grand juries work, generally speaking, is you bring in what’s called a summary witness. You’re going to bring in your investigating agent, you’re going to bring in your lead agent maybe, and they are going to summarize the evidence for the grand jury.”

The big picture idea is that a grand jury probably doesn’t need to see or hear the aspects of classified information the government guards most closely.

Because the grand jury is unlikely to hear top secret information, it will be able to conduct its business in the normal grand jury room, which would typically be secure and private, Lonergan said. The grand jury would not have to use a SCIF – Sensitive Compartmented Information Facility – the highly secure rooms which are designed to defeat surveillance efforts, she said.

“What the government is most concerned about is protecting its sources and methods, not necessarily the content of the conversation that two people had. So you can tell the grand jury about the content of this conversation without telling them exactly how you know it,” she said. “And there you are presenting classified information, but you’re not presenting the most dangerous kind of class info to the grand jury, in case some grand juror doesn’t really abide by their obligation and starts talking to somebody.”