A federal judge has begun an investigation into leaks to newspapers about the secret grand jury that indicted four former Minneapolis police officers on charges of violating the civil rights of George Floyd.

U.S. District Judge Patrick Schiltz ordered the U.S. Attorney's Office and the Minnesota attorney general to provide a list of every person to whom they disclosed grand jury activity.

He also ordered the U.S. Attorney's Office to explain why he shouldn't appoint an independent prosecutor to investigate and file criminal contempt of court charges for the disclosures. Schiltz wants the responses filed under seal no later than June 4.

At issue are stories published by the Star Tribune and the New York Times detailing the possibility of federal charges against the former police officers in Floyd's murder.

On April 29, the Star Tribune published a story with the headline, "Feds plan to indict Chauvin, three other ex-officers on civil rights charges." On Feb. 23, the New York Times published a story about the grand jury with the headline, "With New Grand Jury, Justice Department Revives Investigation Into Death of George Floyd."

The New York Times story came out days before the beginning of jury selection in the state trial of Derek Chauvin, the officer who knelt on Floyd's neck and was convicted in April of second-degree murder, third-degree murder and manslaughter.

Former officers J. Alexander Kueng, Thomas Lane and Tou Thao face charges of aiding and abetting second-degree murder and manslaughter. The three are scheduled to stand trial in state court next March.

Days after Chauvin's conviction, the Star Tribune story revealed that the Justice Department had been working to indict him on federal charges, and if he had been acquitted in state court, the feds planned to arrest him at the courthouse, the story said, citing an unidentified source.

But Chauvin was convicted in state court and on May 8, the four former officers were indicted by the federal grand jury.

In his five-page order signed May 5, Schiltz cited the U.S. Supreme Court's reasons for protecting the secrecy of grand jury proceedings: preventing the escape of those indicted, influence on deliberations, perjury or jury tampering.

"In order to safeguard the secrecy of grand jury proceedings, federal prosecutors are generally prohibited from disclosing matters occurring before a grand jury," Schiltz wrote.

In this case, federal prosecutors were given permission to provide information to Attorney General Keith Ellison's office, which is handling the prosecution of the four former officers. Ellison's office then was prohibited from disclosing the information for anything other than investigative or prosecutorial reasons, Schiltz noted.

Jane Kirtley, professor and director of the Silha Center for Media Ethics and Law, said Schiltz appears to be conducting an investigation to find the source of the leaks without compelling journalists to divulge their sources.

"There's always a risk they'll conclude they have no recourse other than to go to the journalists," she said. "Let's hope that doesn't become necessary."

Star Tribune Managing Editor Suki Dardarian said, "I have no comment on the court's actions, but I will say that the Star Tribune stands resolutely behind its pledge not to reveal the identities of anonymous sources."

A spokeswoman for the New York Times declined to comment.

A similar leak investigation is playing out in state court where Hennepin County District Judge Peter Cahill "suggested" that attorneys for all the parties file sworn affidavits attesting that they weren't the source for a New York Times story earlier in February. Cahill did not order that they must file affidavits.

In that story, the Times cited anonymous sources in reporting that in the days following Floyd's murder, Chauvin was prepared to plead guilty to third-degree murder and go to prison for more than 10 years but then-U.S. Attorney General Bill Barr rejected the deal.

In a hearing in the state case last week, a frustrated Cahill said he first asked attorneys in February to voluntarily file affidavits and was disappointed that only Assistant Attorney General Matthew Frank had complied. Cahill strongly encouraged attorneys last week to follow suit, prompting Frank and Assistant Hennepin County Attorney Joshua Larson to say they would provide affidavits for their offices.

Many attorneys have submitted sworn and notarized affidavits in the state case. Hennepin County Attorney Mike Freeman, however, submitted a general letter saying no one in his office was the source of the leak.

Freeman's office said Friday that he will not file a sworn affidavit.

"The Hennepin County Attorney's Office has informed the court that our office was not the source of any information 'leak' to the New York Times," said a statement from Freeman's office. "Whether it is in the form of a letter or affidavit, County Attorney Mike Freeman has addressed the issue personally and on behalf of his office. At this point, our office feels that we have satisfied the court's request."

Ellison filed a sworn affidavit Friday. Ellison's spokesman, John Stiles, said Friday that they would also file affidavits in the federal matter.

A spokeswoman from the U.S. Attorney's Office declined to comment.

Staff writer Chao Xiong contributed to this report.

Rochelle Olson • 612-673-1747

Twitter: @rochelleolson