Overview
On the morning of 14 February 1929, seven men were lined up against the wall of a garage on North Clark Street in Chicago and shot with submachine guns. Some of the killers were reportedly dressed as police officers, which is the detail that explains why the victims — experienced men in a dangerous trade — stood still to be arranged.
The target was almost certainly George "Bugs" Moran, who ran the North Side operation and who was not in the building. The attribution to Al Capone was immediate and has never really been dislodged. It has also never been proved.
No one was tried for the killings. Capone was in Florida, and was never questioned about them.
The case for Capone
The motive is the strongest part. Capone and Moran were rivals in the same business in the same city, and eliminating Moran would have consolidated Chicago bootlegging under one organisation. Capone had the resources, the men and — on the evidence of the preceding years — no objection in principle.
Historians of the period who have examined it closely tend to conclude that the operation was his, while separating that from the question of his personal presence. The distinction usually drawn is that Capone did not fire a weapon and was not in the state, but that a killing of this scale in this territory would not have proceeded without his authorisation. On that view his Florida alibi is not exculpatory but the point: it is what an alibi is for.
What the physical evidence showed
The forensic thread runs away from Chicago. In December 1929, police raided the Michigan home of Fred "Killer" Burke, a gunman associated with the St Louis outfit Egan's Rats, which had worked with Capone's organisation. Two Thompson submachine guns were recovered.
Calvin Goddard, a pioneer of firearms identification, matched them to the cartridge cases from the garage. This was among the earliest uses of comparison ballistics in a major American case, and it is the one piece of hard evidence anyone has.
It did not lead to a trial for the massacre. Burke was arrested in 1931 for killing a police officer in Michigan and was never extradited to Illinois or charged over North Clark Street.
The informant account, and its problems
The most detailed narrative came later from Byron Bolton, who told the FBI he had been one of the lookouts and named a crew: Burke, Fred Goetz, Gus Winkler, Raymond Nugent and Bob Carey.
That account is the backbone of most modern reconstructions, and it is also the weakest link. Bolton was an informant with reasons to be useful, several of the men he named were dead by the time he spoke, and none of it was tested in court. Historians use it because there is nothing better, while noting that a story nobody cross-examined is a poor foundation for a settled conclusion.
The alternatives
A persistent minority account gives the leading role to the Purple Gang of Detroit, either acting for Capone or acting with him, and points to the difficulty of moving an unfamiliar crew through Chicago unnoticed.
A narrower theory holds that the killing was not primarily about territory at all but a settling of a specific score, with the scale chosen for its effect on everyone watching.
And there is the reading that the police uniforms were not a disguise — that some of the men were what they appeared to be. Chicago policing in the period was corrupt enough for the suggestion to be taken seriously at the time, though no evidence has ever supported it.
Why it stays unsettled
The massacre is the most famous unsolved crime of the era, and the reason is structural rather than mysterious. The witnesses were criminals, the investigators were in some cases bought, the principal suspect was never interviewed, and the man whose guns did the killing was convicted of something else in another state.
What survives is a confident attribution resting on motive and a plausible informant, and a forensic finding that identifies the weapons but not the hand that ordered them used.