The Justice Department is conducting a sweeping review of more than 1,000 grand jury presentations by Illinois prosecutors following revelations of misconduct in a high-profile case.

The review, which includes proceedings going back nearly 20 years, was triggered after charges were dropped against activists involved in protests during an immigration crackdown in Chicago.

Prosecutors were found to have engaged in improper conduct, including a meeting with a grand juror outside official proceedings and the exclusion of dissenting jurors.

U.S. Attorney Andrew Boutros said the effort is intended to ensure ethical conduct and restore confidence that other cases were not compromised, NBC News has reported.

The dismissed case drew scrutiny after transcripts revealed internal grand jury tensions and criticism of the prosecution’s presentation.