On Memorial Day 1937, unionists, their families and sympathisers gathered at Sam's Place, a former tavern and dance hall at 113th Street and Green Bay Avenue, that served as the headquarters of the SWOC.

[1][2] There was an outdoor picnic lunch, speakers, and songs, and some estimate the crowd was between 1,500 to 2,500 including picketers and their families, strike sympathizers, and curious passersby.

"[5] Ten union demonstrators were killed:[6][7][8][9] In the wake of the massacre, newsreel footage of the event was suppressed for fear of creating, in the words of an official at Paramount News agency, "mass hysteria."

Initial news coverage of the event instead framed the crowd as a violent threat to social order, arguing that police merely acted in self-defense.

Still photographs were published in major newspapers such as the Chicago Tribune along with captions such as: "At the Height of the Battle--Here are policemen using their nightsticks and tear gas to subdue the attackers.