The story behind the night Billy McSwiggin was killed in front of The Pony Inn:
"Back in Chicago at the beginning of 1926, Capone was in excellent spirits. Not only had he made his mark in New York, but his whiskey deal would change the face of interstate transportation. Young men with a thirst for adventure and the need for money made a good living working as one of Capone's truckers.
"Doherty's car broke down and they hitched a ride with bootlegger "Klondike" O'Donnell, a bitter enemy of Capone. The four Irish lads went on a drinking binge in Cicero with O'Donnell and his brother Myles and ended up at a bar [this would be The Pony Inn operated by Harry Madigan] close to the Hawthorne Inn where Capone was having dinner. O'Donnell's cruising around in Cicero was a territorial insult.
"Capone and his henchmen, not realizing that McSwiggin was in the bar with Myles O'Donnell, waited outside in a convoy of cars until the drunken men staggered out. Then out came the machine guns and McSwiggin and Doherty were dead.
"Capone was blamed. Despite the blot on McSwiggin's integrity for keeping company with bootleggers, sympathy was with the dead young prosecutor. There was a big outcry against gangster violence and public sentiment went against Capone.
"While everyone in Chicago just knew that Al Capone was responsible, there was not a shred of proof and the failure of this high-profile investigation to return an indictment was an embarrassment to local officials. Police took out their frustrations on Capone's whorehouses and speakeasies which endured a series of raids and fires."
Source: Al Capone: Chicago's Most Infamous Mob Boss, by