Moran's second in command and brother-in-law Albert Kachellek (alias James Clark) was killed along with Adam Heyer, the gang's bookkeeper and business manager; Albert Weinshank, who managed several cleaning and dyeing operations for Moran; and gang enforcers Frank Gusenberg and Peter Gusenberg.

Chicago police officers arrived at the scene to find that victim Frank Gusenberg was still alive, despite having sustained 14 bullet wounds.

[6] Moran was the last survivor of the North Side gunmen; his succession had come about because his similarly aggressive predecessors, Hymie Weiss and Vincent Drucci, had been killed in the violence that followed the murder of their original leader, Dean O'Banion.

Earlier in the year, North Sider Frank Gusenberg and his brother Peter unsuccessfully attempted to murder Jack McGurn.

It is usually assumed that the North Siders were lured to the garage with the promise of a stolen, cut-rate shipment of whiskey, supplied by Detroit's Purple Gang, which was associated with Capone.

The Gusenberg brothers were supposed to drive two empty trucks to Detroit that day to pick up two loads of stolen Canadian whisky.

He and fellow gang member Ted Newberry were approaching the rear of the warehouse from a side street when they saw a police car nearing the building.

North Side Gang member Willie Marks also spotted the police car on his way to the garage and ducked into a doorway and jotted down the license number before leaving the neighborhood.

The two fake police officers carried shotguns and entered the rear portion of the garage, where they found members of Moran's gang and associates Reinhart Schwimmer and John May, who was fixing one of the trucks.

[10] Within days, Capone received a summons to testify before a Chicago grand jury on charges of federal Prohibition violations, but he said he was too unwell to attend.

[11] It was common knowledge that Moran was hijacking Capone's Detroit-based liquor shipments, and police focused their attention on Detroit's predominantly Jewish Purple Gang.

They picked out mugshots of Purple Gang members George Lewis, Eddie Fletcher, Phil Keywell, and his younger brother Harry, but they later wavered in their identification.

On February 22, police were called to the scene of a garage fire on Wood Street where they found a 1927 Cadillac sedan disassembled and partially burned, and determined that the killers had used the car.

Police could not turn up any information about persons named James Morton or Frank Rogers, but they had a definite lead on one of the killers.

Just minutes before the killings, a truck driver named Elmer Lewis had turned a corner a block away from 2122 North Clark and sideswiped a police car.

Police raided Burke's bungalow and found a large trunk containing a bullet-proof vest, almost $320,000 in bonds recently stolen from a Wisconsin bank, two Thompson submachine guns, pistols, two shotguns, and thousands of rounds of ammunition.

On January 8, 1935, FBI agents surrounded a Chicago apartment building at 3920 North Pine Grove looking for the remaining members of the Barker Gang.

The FBI had no jurisdiction in a state murder case, so they kept Bolton's revelations confidential until the Chicago American newspaper reported a second-hand version of his confession.

The newspaper declared that the crime had been "solved", despite being stonewalled by J. Edgar Hoover and the FBI, who did not want any part of the massacre case.

said that the plan to murder Bugs Moran had been plotted in October or November 1928 at a Couderay, Wisconsin resort owned by Fred Goetz.

Present at this meeting were Goetz, Al Capone, Frank Nitti, Fred Burke, Gus Winkler, Louis Campagna, Daniel Serritella, William Pacelli, and Bolton.

Bolton guessed that the actual killers had been Burke, Winkeler, Goetz, Bob Carey, Raymond "Crane Neck" Nugent, and Claude Maddox (four shooters and two getaway drivers).

A Peerless Motor Company sedan had been found near a Maywood house owned by Claude Maddox in the days after the massacre, and in one of the pockets was an address book belonging to victim Albert Weinshank.

His claims were corroborated by Gus Winkeler's widow Georgette in an official FBI statement and in her memoirs, which were published in a four-part series in a true detective magazine during the winter of 1935–36.

Bank robber Alvin Karpis later said to have heard secondhand from Ray Nugent about the massacre and that the "American Boys" were paid a collective salary of $2,000 a week plus bonuses.

Legend states that Capone produced a baseball bat at the climax of a dinner party thrown in their honor and beat the trio to death.

[12] In 1995 Chicago criminologist Arthur Bilek, who had researched the massacre through FBI files and court transcripts for 30 years, named the participants in the massacre to have been Capone henchmen "Machine Gun" Jack McGurn, who assembled the murder team that included lookouts Byron Bolton, Jimmy Moran (no relation to Bugs) and Jimmy McCryssen.

Their job was to watch the garage and alert Tony Accardo and the other triggermen—Fred Burke, Gus Winkler, Freddie Goetz and Robert Carey—when Bugs Moran appeared at the site.

[13][14] Police tested the two Thompson submachine guns (serial numbers 2347 and 7580) found in Fred Burke's Michigan bungalow and determined that both had been used in the massacre.