High Quality Content by WIKIPEDIA articles! The Haymarket affair (also known as the Haymarket massacre or Haymarket riot) was a demonstration and unrest that took place on Tuesday May 4, 1886, at the Haymarket Square in Chicago. It began as a rally in support of striking workers. An unknown person threw a dynamite bomb at police as they dispersed the public meeting. The bomb blast and ensuing gunfire resulted in the deaths of eight police officers, mostly from friendly fire, and an unknown number of civilians. In the internationally publicized legal proceedings that followed, eight anarchists were tried for murder. Five men were convicted, of whom four were executed and one committed suicide in prison, although the prosecution conceded none of the defendants had thrown the bomb.