MINNEAPOLIS — Federal prosecutors in Minneapolis have convened a grand jury and called police witnesses to testify over the past week in connection to a civil rights investigation into Derek Chauvin, signaling a renewed push in the Justice Department's case as the former police officer prepares for trial in state court in the killing of George Floyd, according to sources familiar with the secret proceedings.

The federal investigation into Chauvin involves a 2017 arrest in which Chauvin allegedly jammed his knee into the back of a 14-year-old boy for several minutes while ignoring his pleas that he couldn't breathe — an episode state prosecutors said bore a striking resemblance to Chauvin's conduct in his fatal encounter with George Floyd, according to the sources, who were not authorized to speak on the record. The 2017 case has been deemed inadmissible by the judge in Chauvin's upcoming trial, which will begin next month, but was made public in court documents.

Last summer, the Justice Department promised a robust investigation into Chauvin and three other officers implicated in Floyd's death, as anti-police brutality riots tore through the Twin Cities and spread across the United States. On May 28, outside the FBI field office in Brooklyn Center, Minnesota U.S. Attorney Erica MacDonald said the federal investigation would focus on whether the officers used their authority as law enforcement agents to deprive Floyd of his constitutional rights. To meet the bar of this federal civil rights violation, investigators must prove the officers took action — or failed to do so — with knowledge of wrongdoing.

At the time, MacDonald, calling the case a top priority for the Justice Department, said the federal investigation "must be done right" and it could take time to build. The federal case has been quiet until the recent empaneling of the grand jury — a private proceeding in which a group of citizens decided whether a charge is warranted — a revelation first reported by The New York Times and confirmed by Star Tribune sources Tuesday, Feb. 23.

Chauvin is facing a trial next month on charges of second-degree murder and manslaughter in state court. He was arrested after bystander videos showed him kneeling on Floyd's neck for more than nine minutes. Former Officers J. Alexander Kueng, Thomas Lane and Tou Thao are each charged as accomplices.

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The Justice Department investigation runs parallel to the state case, meaning it could proceed regardless of the verdict on the upcoming state trials for Chauvin and the others.

The U.S. attorney's office declined to comment for this story. A spokesman for the Minneapolis Police Department did not immediately respond to requests for comment on the proceedings.

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