The soldiers’ trial started November 27th and lasted until December 5th.
The defense of the soldiers was complicated by the acquittal of Thomas Preston since the jurors would be inclined to believe the soldiers were responsible for the shootings. As a result the defense focused on the actions of the mob that threatened the soldiers in order to pursue a justifiable use of force in self defense. Adams argued that if the soldiers were attacked by “a motley rabble of saucy boys, negroes and molattoes, Irish teagues and outlandish jacktars,” At most, Adams argued, the soldiers were guilty of manslaughter and not of murder.
An important circumstance in the trial was the death bed testimony of Patrick Carr. Carr had been wounded on March 5th, and before he died he admitted to his physician, John Jeffries, that the soldiers were provoked and fired in self defense and that he (Patrick Carr) did not blame the soldier who shot him.
The prosecution concentrated on showing that soldiers wanted revenge after many months of being abused and harassed by townspeople. A witness testified that Private Killroy had admitted to him that “he would not miss an opportunity to fire on inhabitants”. However, the prosecution’s case was undermined on cross-examination when witnesses admitted that the crowd was throwing objects and provoking the soldiers to fire.
In his summation, Adams famously argues:
I will enlarge no more on the evidence, but submit it to you.—Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passions, they cannot alter the state of facts and evidence: nor is the law less stable than the fact; if an assault was made to endanger their lives, the law is clear, they had a right to kill in their own defence; if it was not so severe as to endanger their lives, yet if they were assaulted at all, struck and abused by blows of any sort, by snow-balls, oyster-shells, cinders, clubs, or sticks of any kind; this was a provocation, for which the law reduces the offence of killing, down to manslaughter, in consideration of those passions in our nature, which cannot be eradicated. To your candour and justice I submit the prisoners and their cause.
The jury acquitted six of the soldiers: William Wemms, William M’Cauley, Hugh White, William Warren, John Carrol and James Hartegan. The other two soldiers, Hugh Montgomery and Matthew Killroy, were found not guilty of murder but guilty of manslaughter, therefore escaping the death penalty. Both men invoked the “benefit of the clergy” allowing them to avoid a long imprisonment. They had their thumbs branded with the letter “M”, leaving a permanent mark so that they would not receive a lenient treatment in the future.
On December 13th, the four civilians who were accused of firing from the customs house were tried. All four were acquitted as the only prosecution witness presented a false testimony. The witness was later convicted of perjury.