The term sounds odd to modern ears, but it was an old military phrase, in use since the Civil War, and further evidence of how Chicago's militarized police force understood the riot. A dead line was a line, often invisible, drawn around a military prison. Any prisoner seen outside the dead line would be shot on sight.
In case there was any question, it quickly became clear who the police believed the “prisoners” they needed to control were. Although officers were told to make sure that whites stayed west of Wentworth all the way down to Sixty-Third Street and that no Blacks crossed Wentworth heading west, they spent most of the riot enforcing the second part of that order while ignoring the first.
If the creation of the dead line seemed to contradict official claims that everything was under control, it was consistent with the fear mongering reports in Chicago’s mainstream newspapers. The Herald-Examiner described turmoil on the streets of South Side neighborhoods where “Negroes and whites normally comingle” and reported that a mob of several thousand Black men had laid siege to an armory, seizing hundreds of weapons.
Throughout the riots, the Herald-Examiner’s coverage was exaggerated and inflammatory. But in this article, it offered a racist distinction that was common in Chicago's white press: Inside Black neighborhoods, lawless Blacks attacked whites for no reason. In white neighborhoods, whites used self-defense to protect themselves from Black invaders.
During the riot, other white papers emphasized the dangers the Black community posed to order even as they described the violence Black victims endured at the hands of white mobs. Even those papers that admitted Black individuals were trying to defend themselves were quick to remind everyone that they were heavily armed: as the New York Times reported, “it was admitted,” by whom was unclear, that “many of the negroes possessed arms of one kind or another and were prepared to defend themselves against aggression."