There were two additional important results of the "massacre" and the trial.  First, because the defense of the soldiers was led by John Adams, one of the most important members of the revolutionary movement, it became obvious to both the British and the American colonists that the rule of law was more important than one's political beliefs.  Adams, who interviewed dozens of witnesses, proved that the crowd initiated the violence and that the soldiers believed their lives were in danger.  Even though Adams was relentlessly criticized by many colonials for his defense of the British soldiers, the British--and even many pro-revolution Americans--understood that Adams' loyalty was to the law rather than his own politics.  Second, Adams' defense indicated that some of Boston's leading citizens were implicated in inciting others to violence, which was a capital crime under British law--that is, these people were guilty of treason and could be executed if proven guilty.  In short, the leaders who were advocating violence understood they could be accused of treason.   Among other things, Adams uncovered a significant amount of sympathy among Americans for the British and against the revolutionary movement.   When the leading members of the revolutionary movement realized the extent of American sentiment against rebellion, they realized that the time was not ripe for a physical break with Great Britain, and they took steps to moderate the violence they had encouraged before the massacre.  

The Boston Massacre was an incident in Boston, Massachusetts in 1770 in which 5 American colonists were killed by British soldiers.  It was hugely important as a subject of propaganda for the Americans who were pushing for more independence from Britain.

Since late 1768, British soldiers had been in Boston to keep the peace.  Soldiers in those days were not very well-disciplined and were often likely to treat civilians poorly.  They were also poorly-paid and competed with civilians for jobs that they tried to work while not on duty.  Finally, the civilians were also required to house and feed the soldiers.  All of this meant that there was a lot of hatred between the two sides.

In March of 1770, an incident erupted between soldiers and civilians.  Civilians started doing things like throwing rocks, ice, and snow at the soldiers.  The soldiers shot into the crowd.  Three civilians were killed outright and two died later of their wounds.

The “massacre” was very important because of how well the American patriots used it.  They portrayed it as an unprovoked massacre of innocent civilians.  This helped turn many American colonists against the British.  Thus, the massacre was an important incident that helped lead more Americans to desire independence from Britain.