Cook County Coroner Herman Bundesen carefully collected the evidence from the crime scene. He also named a coroner’s jury consisting of local business leaders to investigate the murders.

The jury’s first concern was to figure out whether police officers actually were involved in the Massacre. They hired Dr. Calvin Goddard, a pioneer in ballistics testing from New York, to work on the case.

When Goddard arrived, he was presented with a massive collection of bullets and shell casings recovered from the crime scene, including 70 .45-caliber cartridge shells.

He quickly determined the .45-caliber shells had been fired from Thompson submachine guns. He concluded that 50 cartridges had been fired from one Thompson and 20 from another.

Goddard’s first task was to answer the question of whether police weapons were used in the Massacre. He obtained samples of fired bullets from several Thompson submachine guns owned by the Chicago Police Department. After he compared them under a microscope with the slugs removed from the murder victims, he informed the coroner’s jury that no police weapons had been used. This led investigators to believe the shooters had worn police uniforms as a disguise.

A few months later, the murder of a sheriff’s deputy in rural Michigan led to a cache of weapons in the house of the suspect, Fred “Killer” Burke. Two Tommy guns confiscated from the house were tested by Goddard and were proved to have been used in the Massacre.