When a bomb killed seven policemen at a Haymarket Square labor rally on May 4, 1886, Chicago answered with the classic political trial: eight anarchists — August Spies, Albert Parsons, Adolph Fischer, George Engel, Louis Lingg, Samuel Fielden, Michael Schwab, and Oscar Neebe — were convicted of murder although the bomb-thrower was never identified and most were not present when it exploded. The prosecution's theory was that their speeches and newspapers had inspired the unknown killer; the jury was openly biased, and Judge Joseph Gary's rulings made the trial a referendum on anarchism itself.
Seven were sentenced to death. On November 11, 1887 — "Black Friday" to the labor movement — Spies, Parsons, Fischer, and Engel were hanged; Lingg had died in his cell the day before. Spies's last words from the scaffold, "there will come a time when our silence will be more powerful than the voices you strangle today," became the international labor movement's epitaph for the case, and May Day itself was established in the executed men's memory.