Federal prosecutors have dropped all criminal charges against four activists who were indicted in October for protesting outside a suburban Chicago immigration detention center.

U.S. Attorney Andrew Boutros announced the decision Thursday following a hearing that addressed concerns about prosecutorial misconduct related to grand jury proceedings. The activists were among a group known as the "Broadview Six" who demonstrated outside the federal immigration facility during last year's immigration enforcement operations.

The unusual development occurred after issues arose regarding redactions made by prosecutors to grand jury transcripts. A top federal prosecutor appeared to acknowledge misconduct in the grand jury process during the proceedings, though specific details of the alleged misconduct were not immediately disclosed.

The case represents another instance of criminal charges related to Trump administration immigration enforcement unraveling in federal court. Prosecutors may now face potential sanctions over their handling of the grand jury materials.

The four defendants had originally faced federal charges stemming from their October protest activities outside the immigration detention facility in the Chicago suburbs. The specific nature of the original charges and the timeline of events leading to Thursday's dismissal were not detailed in court records immediately available.