It began as a peaceful rally in support of workers striking for an eight-hour day and in reaction to the killing of several workers by the police. An unknown person (there are theories that it was a police agitator trying to cause an incident however this is unconfirmed and probably incorrect) threw a dynamite bomb at police. The bomb blast and gunfire resulted in the deaths of seven police officers and at least four civilians; dozens of others were wounded.
- "Originally at the corner of Des Plaines and Randolph". Cityofchicago.org. Archived from the original on May 6, 2009. Retrieved March 18, 2012.
- Timothy Messer-Kruse, The Haymarket Conspiracy: Transatlantic Anarchist Networks (2012)
- Smith, Carl. "Act III: Toils of the Law". The Dramas of Haymarket. Chicago Historical Society and Northwestern University. Retrieved December 30, 2017.
- Trachtenberg, Alexander (March 2002) . The History of May Day. Marxists.org. Retrieved January 19, 2008.
- "Site of the Haymarket Tragedy". City of Chicago Department of Planning and Development, Landmarks Division. 2003. Archived from the original on July 14, 2006. Retrieved January 19, 2008.