On the morning of Thursday, February 14, 1929 St. Valentine's Day, six members of George 'Bugs' Moran's gang and a mechanic who happened to be at the scene were lined up against the rear inside wall of the garage of the SMC Cartage Company in the Lincoln Park neighborhood of Chicago's North Side. They were then shot and killed by four members of Capone's gang (two of them dressed as police officers). When one of the dying men, Frank Gusenberg, was asked who shot him, he replied, "Nobody shot me."[1] Capone himself had arranged to be on vacation in Florida at the time.

The St. Valentine's Massacre resulted from a plan devised by Al Capone and various members of his gang, for Jack "Machine Gun" McGurn, Fred “Killer” Burke and Fred Goetz, to eliminate Bugs Moran, the boss of the North Side Gang and Capone's main rival. The massacre was planned by the Capone mob for a number of reasons; in retaliation for an unsuccessful attempt by Frank and his brother Peter Gusenberg to murder Jack McGurn earlier in the year; the North Side Gang's complicity in the murder of Pasqualino "Patsy" Lolordo as well as Antonio "The Scourge" Lombardo, and Bugs Moran muscling in on a Capone-run dog track in the Chicago suburbs. Also, the rivalry between Moran and Capone for control of the lucrative Chicago bootlegging business led Capone to accept McGurn's plan.

The plan was to lure Moran and his men to the SMC Cartage warehouse on North Clark Street. For decades it has been assumed that the North Side Gang was lured to the garage with the promise of a cut-rate shipment of bootleg whiskey, supplied by Detroit's Purple Gang. However, recent studies indicate this was almost certainly not the case. All seven victims (with one exception) were dressed in their best clothes, hardly suitable for unloading a large shipment of whiskey crates and driving it away. The real reason for the gang gathering in the garage will probably never be known, but it almost certainly wasn't to receive a load of Purple Gang booze.

A four-man team led by Fred Burke would then enter the building, two disguised as police officers, and kill Moran and his men. Before Moran and his boys were set to arrive, Capone placed lookouts in the apartments across the street from the warehouse. Wishing to keep the lookouts inconspicuous, Capone had hired two thugs, Byron Bolton and Jimmy Morand. Mug shots of Purple Gang members Eddie Fletcher, Harry Keywell and his brother Phil, were later picked out by the landlady across the street as the phony roomers. Later, the women who identified them wavered, and both Fletcher and Harry Keywell were cleared by Chicago police. Nevertheless, the mistaken idea that the Purple Gang played a part in the massacre would last for decades.

At around 10:30 a.m. on St. Valentine's day, four members of the Burke gang drove to the warehouse in two cars; a Cadillac sedan and a Peerless, both outfitted to look like detective sedans. Two men were dressed in police uniforms and two in street clothes. The Moran Gang had already arrived at the warehouse. However, Moran himself was not inside. One account states that Moran was supposedly watching the warehouse, spotted the police car, and fled the scene. Another account was that Moran was simply late getting there.

Byron Bolton confused one of Moran's men for Moran himself; he then signaled Burke's men they approached the warehouse. The two phony cops, carrying shotguns, exited the Peerless and entered the warehouse through the two rear doors. Inside they found six members of Moran's gang and a seventh man who was actually a mechanic fixing one of the cars, and not a gangster at all. The killers told the seven men to line up facing the back wall; there was apparently no resistance, as the Moran men thought their captors were real cops.

Then the two "cops" let in two men through the front door facing Clark Street. This pair, riding in the Cadillac, were dressed in civilian clothes. Two of the killers starting shooting with Thompson sub-machine guns. All seven men were killed in a storm of seventy machine-gun bullets and two shotgun blasts according to the coroner's report.

To show by-standers that everything was under control, the pair in street clothes came out with their hands up, led by the two uniformed cops. The only survivor in the warehouse was John May's German Shepherd, Highball. When the real cops arrived, they first heard the dog howling. On entering the warehouse, they found the dog trapped under a beer truck and the floor covered with blood, shell casings, and corpses. The victims were identified as James Clark (AKA Albert Kachellek), Frank Gusenberg, Peter Gusenberg, Adam Heyer, John May, Reinhart Schwimmer, and Al Weinshank.

Commenting later on the massacre, Capone reportedly said "I don't give a damn killing those people."