The invitation appeared in New Orleans newspapers on March 14, 1891.  “All good citizens" were asked to meet near the parish jail and remedy a failure of justice". The last line read:

"Come prepared for action five months earlier, Police Chief David Hennessy had been ambushed while walking home and died the next day. The murder of the city's top lawman by gunmen who vanished stunned New Orleans. Police arrested more than 100 Italians, and the mayor called the killing "Sicilian vengeance". Nine men went on trial. Six were acquitted, and the jury deadlocked on three. Hennessy's killers were never officially identified. However, newspapers blamed the verdict almost immediately on a secret Mafia that had supposedly bought the jury. By ten o'clock the next morning, people were packed so tightly around the prison entrance that streetcars could not move. William Parkerson, a lawyer and former mayoral campaign manager, addressed them. Thousands then followed him to the jail. Guards released the Italian prisoners from their cells and told them to hide. An armed group broke through a side door with beams and axes. Eleven Italian men were killed that day. Two were hanged outside, nine were shot or beaten to death within the prison. None had been convicted of murdering Police Chief David Hennessy.

Some of those killed had not yet been tried. Italy demanded punishment and compensation for its citizens. Washington could not deliver the first: murder was a Louisiana matter, and Louisiana was not going to prosecute. Italy recalled its minister from the United States. Washington withdrew its representative from Rome. And the relations remained broken for more than a year. It was President Benjamin Harrison who eventually condemned the massacre and sent Italy 125,000 francs, about $25,000 then, for the victims' families. Italy accepted the payment and officially restored diplomatic relations in April of 1892.

To this day, no one who organized or carried out the killings has ever been punished.