Skip Yates was in his home office when he heard screams and the shrill whistles Chicagoans have been blowing to signal immigration agents are nearby. He peered from his veranda to see large vehicles and tear gas wafting down the street. Yates shut the door as he began coughing, his eyes burning.

The Department of Justice has abruptly moved to dismiss the indictment against two people accused last month of "ambushing" federal agents conducting an immigration sweep in Chicago, including a woman who was shot five times in the incident.