On this date in 1920, a paymaster and a security guard are killed during a mid-afternoon armed robbery of a shoe company in South Braintree, Massachusetts.

Out of this rather unremarkable crime grew one of the most famous trials in American history and a landmark case in forensic crime detection. Both Fred Parmenter and Alessandro Berardelli were shot several times as they attempted to move the payroll boxes of their New England shoe company. The two armed thieves, identified by witnesses as “Italian-looking,” fled in a Buick. The car was found abandoned in the woods several days later. Through evidence found in the car, police suspected that a man named Mike Boda was involved. However, Boda was one step ahead of the authorities, and he fled to Italy.

Police did manage to catch Boda’s colleagues, Nicola Sacco and Bartolomeo Vanzetti, who were each carrying loaded weapons at the time of their arrest. Sacco had a .32 caliber handgun–the same type as was used to kill the security guards–and bullets from the same manufacturer as those recovered from the shooting. Vanzetti was identified as a participant in a previous robbery attempt of a different shoe company. Sacco and Vanzetti were anarchists, believing that social justice would come only through the destruction of governments. In the early 1920s, mainstream America developed a fear of communism and radical politics that resulted in a anti-communist, anti-immigrant hysteria. Sacco and Vanzetti, recognizing the uphill battle ahead, tried to put this fear to their advantage by drumming up support from the left wing with claims that the prosecution was politically motivated. Millions of dollars were raised for their defense by the radical left around the world. The American embassy in Paris was even bombed in response to the Sacco-Vanzetti case; a second bomb intended for the embassy in Lisbon was intercepted.

The well-funded defense put up a good fight, bringing forth nearly 100 witnesses to testify on the defendants’ behalf. Ultimately, eyewitness identification wasn’t the crucial issue; rather, it was the ballistics tests on the murder weapon. Prosecution experts, with rather primitive instruments, testified that Sacco’s gun was the murder weapon. Defense experts claimed just the opposite. In the end, on July 14, 1921, Sacco and Vanzetti were found guilty; they were sentenced to death.

However, the ballistics issue refused to go away as Sacco and Vanzetti waited on death row. In addition, a jailhouse confession by another criminal fueled the controversy. In 1927, Massachusetts Governor A. T. Fuller ordered another inquiry to advise him on the clemency request of the two anarchists. In the meantime, there had been many scientific advances in the field of forensics. The comparison microscope was now available for new ballistics tests and proved beyond a doubt that Sacco’s gun was indeed the murder weapon. Sacco and Vanzetti were executed in August 1927, but even the new evidence didn’t completely quell the controversy. In October 1961, and again in March 1983, new investigations were conducted into the matter, but both revealed that Sacco’s revolver was indeed the one that fired the bullet and killed the security guards. On August 23, 1977, Massachusetts Governor Michael Dukakis issued a proclamation that Sacco and Vanzetti had not received a fair trial.