WASHINGTON (Reuters) - Attorney General William Barr has pledged to release next week Special Counsel Robert Mueller’s report on Russia’s role in the 2016 U.S. election and contacts between Moscow and President Donald Trump’s campaign, albeit with color-coded redactions.

FILE PHOTO: U.S. President Donald Trump heads back to the Oval Office after declaring a national emergency at the U.S.-Mexico border during remarks about border security in the Rose Garden of the White House in Washington, U.S., February 15, 2019. REUTERS/Carlos Barria/File Photo

While congressional Democrats have demanded the release of the full report with nothing blacked out, as well as the underlying evidence Mueller collected, Barr has said he will redact four categories of sensitive information.

Barr told a congressional committee on Tuesday these redactions will be color-coded and accompanied by notes explaining the grounds for withholding information. It is unclear how much will be blacked out.

According to a March 24 letter Barr sent to lawmakers, Mueller’s nearly 400-page report presents evidence on both sides of the question of whether Trump engaged in obstruction of justice, and while it “does not conclude that the president committed a crime, it also does not exonerate him.”

Barr said in his letter that Mueller did not establish that the Trump campaign engaged in a criminal conspiracy with Russia. Barr also said that he as attorney general concluded that Mueller’s evidence was “not sufficient” to establish that Trump committed criminal obstruction of justice.

Here is an explanation of the four categories of information that Barr has said will be redacted.

GRAND JURY MATERIAL

In the U.S. criminal justice system, prosecutors generally must get authorization from a group of citizens known as a grand jury before bringing criminal charges or issuing subpoenas. Grand juries meet in secret to ensure that people being investigated are not tipped off, while also protecting the privacy of potential criminal defendants who ultimately are not charged.

Over the course of Mueller’s investigation, which led to charges against 34 people and three Russian companies, his team used grand jury proceedings to issue more than 2,800 subpoenas and executed nearly 500 search warrants. A provision of the Federal Rules of Criminal Procedure called Rule 6(e) requires government lawyers to maintain the confidentiality of “matters” before grand juries, with some exceptions.

This rule is unlikely to lead to many redactions in the part of the Mueller report dealing with whether Trump committed the crime of obstruction of justice with actions aimed at impeding the inquiry. For that investigation, Mueller’s team gathered evidence through voluntary FBI interviews with witnesses, which do not implicate grand jury secrecy rules.

Mueller did use a grand jury to question associates of Roger Stone, a longtime adviser to Trump who came under scrutiny due to his interactions with the Wikileaks website that published emails the special counsel has said were hacked by Russia to harm Democratic candidate Hillary Clinton. In January, Mueller indicted Stone on charges including obstruction of an official proceeding, witness tampering and making false statements. Stone has pleaded not guilty.

Another key figure who testified before Mueller’s grand jury was George Nader, a Lebanese-American businessman involved in an effort to set up a back channel between the incoming Trump administration and the Kremlin while Barack Obama was still president, according to a Washington Post report.

INFORMATION THAT COULD AFFECT ONGOING CASES

Barr has said he will redact information that could interfere with ongoing prosecutions.

“You’ll recall that the special counsel did spin off a number of cases that are still being pursued,” Barr told lawmakers. “And we want to make sure that none of the information in the report would impinge upon either the ability of the prosecutors to prosecute the cases, or the fairness to the defendants.”

Mueller’s team has enlisted attorneys from other parts of the Justice Department, court records show, to jointly prosecute certain ongoing cases. These include: charges against Stone; witness-tampering charges against Konstantin Kilimnik, a Russian associate of Trump’s former campaign chairman Paul Manafort; charges against 12 Russian intelligence officers accused of hacking Democratic emails; and a Russian “troll farm” accused of flooding social media sites with propaganda to promote Trump and disparage Clinton.

Separately, referrals by Mueller gave rise to inquiries by federal prosecutors in Washington, Virginia and New York. The New York referral related to Trump’s former personal lawyer Michael Cohen, who pleaded guilty to a variety of charges and is due to report to prison for a three-year sentence in May. U.S. prosecutors in Virginia are investigating secret Turkish lobbying involving Michael Flynn, Trump’s fired former national security adviser. In Washington, lobbyist Samuel Patten pleaded guilty to failing to register as a foreign agent for pro-Russian Ukrainian politicians and helping a pro-Russian Ukrainian businessman illegally purchase tickets to Trump’s inauguration.

Stone’s trial is set to begin in November and Manafort has been hit with state charges in New York, so information about those two men could be redacted.

‘PERIPHERAL THIRD PARTIES’

Barr has said he will redact “information that would unduly infringe on the personal privacy and reputational interests of peripheral third parties.” This is another way of articulating a long-standing Justice Department policy of not releasing disparaging information about a person unless the individual is indicted. The policy is grounded in the belief that people who are indicted can defend themselves in court, but people who are investigated without being charged do not have this opportunity.

This policy has been dispensed with before, including in June 2016 when then-FBI Director James Comey publicly pronounced that Clinton had been “extremely careless” in handling classified information even though she was never charged.

Some legal experts have said this policy should not apply to Mueller’s report because it was primarily a counterintelligence operation, rather than a traditional criminal investigation. By focusing on the privacy rights of “peripheral” third parties, Barr may be signaling he will make an exception to the policy in order to allow information to remain unredacted concerning people who, while not charged with crimes, are central to the probe, potentially including Trump.

INTELLIGENCE-GATHERING SOURCES AND METHODS

In investigating Russian election interference, Mueller’s team may have relied on information from top-secret intelligence sources. Justice Department officials last year turned down a request by Republican lawmakers for certain information about Mueller’s investigation, saying doing so could put lives at risk and expose the identity of a U.S. citizen who provided intelligence to the FBI. While redacting such material, Barr might opt to divulge it to certain lawmakers behind closed doors.