Taken from Weird Chicago:
ST. VALENTINE'S DAY MASSACRE
2122 NORTH CLARK STREET
For a city that is so filled with the history of crime, there has been little preservation of the landmarks that were once so important to the legend of the mob in Chicago. Gone are the landmarks like the Lexington Hotel, where Al Capone kept the fifth floor suite and used the place as his headquarters. But most tragic, at least to crime buffs, was the destruction of the warehouse that was located at 2122 North Clark Street. It was here, on Valentine's Day 1929, that the most spectacular mob hit in gangland history took place..... the St. Valentine's Day Massacre.
The building was called the S-M-C Cartage Company and was a red, brick structure on Clark Street. The events that led to the massacre began on the morning of the 14th. A group of men had gathered at the warehouse that morning, set up by a Detroit gangster who told Moran that a truck was on its way to Chicago.One of them was Johnny May, an ex-safecracker who had been hired by George "Bugs" Moran as an auto mechanic. He was working on a truck that morning, with his dog tied to the bumper, while six other men waited for the truck of hijacked whiskey to arrive. The men were Frank and Pete Gusenberg, who were supposed to meet Moran and pick up two empty trucks to drive to Detroit and pick up smuggled Canadian whiskey; James Clark, Moran's brother-in-law; Adam Heyer; Al Weinshank; and Reinhardt Schwimmer, a young optometrist who had befriended Moran and hung around the liquor warehouse just for the thrill of rubbing shoulders with gangsters.Bugs Moran was already late for the morning meeting. He was due to arrive at 10:30 but didn't even leave for the rendezvous, in the company of Willie Marks and Ted Newberry, until several minutes after that.
While the seven men waited inside of the warehouse, they had no idea that a police car had pulled up outside, or that Moran had spotted the car and had quickly taken cover. Five men got out of the police car, three of them in uniforms and two in civilian clothing. They entered the building and a few moments later, the clatter of machine gun fire broke the stillness of the snowy morning. Soon after, five figures emerged and they drove away. May's dog, inside of the warehouse, was barking and howling and when neighbors went to check and see what was going on... they discovered a bloody murder scene.
Moran's men had been lined up against the rear wall of the garage and had been sprayed with machine-guns. They killed all seven of them but had missed Bugs Moran. He had figured the arrival of the police car to be some sort of shakedown and had hung back. When the machine gunning started, he, Marks and Newberry had fled. The murders broke the power of the North Side gang and Moran correctly blamed Al Capone. No one will probably ever know who the actual shooters were, but one of them was probably Machine Gun McGurn, one of Capone's most trusted men.Surprisingly, while Moran quickly targeted Capone as ordering the hit, the authorities were baffled. Capone had been in Florida at the time of the massacre and when hearing the news, he stated, "the only man who kills like that is Bugs Moran". At the same time, Moran was proclaiming that "only Capone kills guys like that".Moran was right.... Capone had been behind the killing and this was perhaps the act that finally began the decline of Capone's criminal empire. He had just gone too far and the authorities, and even Capone's adoring public, were ready to put an end to the bootleg wars.