The "Boston Massacre" as it is called, was really not a massacre in the sense that a lot of people were slaughtered (because only five people were killed), it was a massacre in the sense that the British government's authority was not going to be tolerated. This incident marked the beginning of the end for England and its presence in the United States of America.
On October 1, 1768 a group of British regulars arrived in Boston, MA. to maintain order. The civilians reacted to the redcoats like they were invaders by taunting them through name calling, spitting, and fighting. The people of Boston had gained control of the reigns of power and prevented the soldiers from carrying out their duties. During the next eighteen months tension mounted between the two sides.
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On March 5, 1770 the Twenty-Ninth Regiment came to the relief of the Eighth on duty at the Customs House on King (now State) Street. The soldiers, led by Captain Thomas Preston, were met by a large and taunting crowd of civilians. Captain Preston was unable to disperse the crowd and as they chanted "Fire and be damned" he ordered his troops "Don't Fire!" With all the commotion the soldiers probably did not hear his orders and they opened fire on the crowd killing three men instantly and another two who died later.
Seven months later, in October of 1770, Captain Preston was tried for murder in a Boston courtroom. He was defended by John Adams and Robert Auchmuty and assisted by Josiah Quincy Jr. Captain Preston was acquitted by a Boston jury. It was never satisfactory explained why the radicals Adams and Quincy represented Preston, and later the soldiers, although some surviving documents suggest that the jury in Preston's case was "packed." When the soldiers case came to trial soon after they were defended by Adams, Quincy, and Sampson Salter Blowers. The jurors in their case came from outside of Boston and they won acquittals a month after the trial began.
Cite in Boston where the massacre took place
Zobel, Miller. Dictionary of American History, Volume I, pg. 345-46.
Faragler, John Mack. The Encyclopedia of Colonial and Revolutionary America pg. 42-43.