Why was the boston massacre a turning point for the american revolution?

It angered the colonists to the point of revolution

The Boston Massacre is considered one of the most significant events that turned colonial sentiment against King George III and British Parliamentary authority. John Adams wrote that the "foundation of American independence was laid" on March 5, 1770, and Samuel Adams and other Patriots used annual commemorations (Massacre Day) to encourage public sentiment toward independence.

It helped America pull away from British rule and establish a new country on it’s own.