10 people died in a suitcase bombing at Stuart and Market during the Preparedness Day Parade (wiki)
The Preparedness Day Bombing was a bombing in San Francisco, California on July 22, 1916, when the city held a parade in honor of Preparedness Day, in anticipation of the United States’ imminent entry into World War I. During the parade a suitcase bomb was detonated, killing ten and wounding forty in the worst such attack in San Francisco’s history. Two labor leaders, Thomas Mooney and Warren Billings, were convicted in separate trials and sentenced to be hanged. Rena Mooney and Israel Weinberg were acquitted.
The parade was captured on film and the aftermath just minutes after the bombing by the Hearst/Pathe news service and is on the Library of Congress youtube channel
also at Fire in the Hole
Images via Calisphere/UC Berkeley archives
Via the New York Times (PDF)