On the morning of February 14, 1929, seven men associated with Chicago's North Side Gang were gathered at a garage at 2122 North Clark Street in the Lincoln Park neighborhood. Between four and six attackers, two dressed as police officers, entered the garage, lined the men against a wall, and shot them with Thompson submachine guns and a sawed-off shotgun. Seventy rounds were fired from the machine guns and one from the shotgun. Six men died at the scene; a seventh, Frank Gusenberg, survived long enough to be questioned by police but refused to identify his attackers before dying.
The victims were Albert Kachellek (alias James Clark), Adam Heyer, Albert Weinshank, Frank Gusenberg, Peter Gusenberg, and two non-gang associates, Reinhardt H. Schwimmer and John May. The killings occurred amid ongoing violent competition for control of Chicago's Prohibition-era bootlegging trade between the North Side Gang, led by George "Bugs" Moran, and the Chicago Outfit, led by Al Capone. Police and historians have speculated the attack was intended to kill Moran himself, who had not yet arrived at the garage when the shooting began.
Multiple bodies investigated the massacre independently, including Chicago police, the Illinois Attorney General's office, and the Cook County coroner's office under Herman Bundesen. Forensic ballistics pioneer Calvin Goddard was engaged to examine shell casings and weapons. Two vehicles believed linked to the crime were later found destroyed. Several men, including Jack McGurn, John Scalise, and Albert Anselmi, were arrested and some charged, but the charges against them were dropped for lack of evidence. The coroner's inquest was closed in 1931 with the conclusion that "the killings were by persons unknown."
In 1935, Byron Bolton, previously identified as a possible lookout at the scene, was arrested on unrelated charges and told the FBI that the shooters were Fred Goetz, Gus Winkler, Fred Burke, Ray Nugent, and Bob Carey, acting on Capone's orders to kill Moran. This account was corroborated by the memoirs of Winkler's widow, Georgette. Some historians have disputed Bolton's account, proposing alternative suspects including "Three Fingered Jack" White and Tony Accardo. Fred Burke was later linked to weapons used in the massacre after a 1929 raid on his home following the killing of a Michigan police officer; he was convicted of that officer's murder and sentenced to life imprisonment, dying in prison in 1940. No one was ever convicted specifically for the Valentine's Day killings.
The massacre contributed to public shock over Prohibition-era gang violence and, along with other Thompson submachine gun-related crimes, influenced the passage of the National Firearms Act of 1934. The garage was demolished in 1967.