the newly-appointed union commander in missouri, brigadier general nathaniel lyon, had learned that the ostensibly neutral state militia training in camp jackson was planning to raid the federal arsenal in st. louis. after capturing the entire unit, lyon marched the captives into town in order to parole them. en route, hostile secessionist crowds gathered, and after an accidental gunshot, lyon's men fired into the mob, killing at least 28 civilians and injuring dozens of others. several days of rioting throughout st. louis followed. the violence ended only after martial law was imposed and union regulars were dispatched to the city.