The prosecution presented the following categories of evidence: eyewitness testimony, ballistics evidence, a cap found near the victims, and the "consciousness of guilt" Sacco and Vanzetti displayed when arrested. Fifty-nine witnesses testified for the Commonwealth, and ninety-nine for the defendants.
There was extensive contradictory testimony from eyewitnesses. Subsequently, Judge Thayer ruled that "these verdicts did not rest, in my judgment, upon the testimny of the eyewitnesses. . . ."
The prosecution claimed that the revolver found on Vanzetti the night of his arrest had been taken from the dying Be4rardelli at the crime scene. Despite inconclusie evidence, the prosecution argued to the jury: "We say in plain English that on the evidence we have proven to you beyond any reasonable doubt . . . that the .38 Harrington & Richardson revolver that was found upon the defendant Vanzetti was the .38 Harrington & Richardson revolver that poor Berardelli tried to draw from his pocket to defend himself. . . ."
The prosecution maintained that the fatal bullet (known as Bullet No. III) fired at Berardelli came from Sacco's Colt pistol.
At trial, State Police Captain William H. Proctor testifed that, in his opinion, Bullet No. III was "consistent with being fired" from Sacco's gun.
Two years later, Captain Proctor signed an affidavit stating he did not believe Sacco's pistol fired bullet No. III, and that he had shared his doubts with Katzmann prior to tesifying. See Exhibit Panel entitled "Motions for a New Trial."
The day after the robbery and murders a grey cloth cap with a torn lining was found near where Berardelli's body had fallen. The prosecution claimed that it resembled one owned by Sacco. Testimony indicated that Saco hung his cap on a nail while at work. Prosecutors claimed that the nail tore the lining. This cap was not the same size as other caps found at Sacco's home. The prosecution asked Sacco to try on the cap. Sacco said it was too small; the prosecution maintained that it fit.
In 1927, prior to the executions, Jeremiah Gallivan, chief of police in Braintree from 1905 to 1926, statd that he had torn the cap's lining to see if he could find inside any marks of identification.