Read the following passage.
The following testimony of the Boston Massacre was given by Captain Thomas Preston during court hearings on the event on March 13, 1770.
I saw the people in great commotion and heard them use the most cruel and horrid threats against the troops. They immediately surrounded the sentry . . . and with clubs and other weapons threatened to execute their vengeance on him. I was soon informed by a townsman their intention was to carry off the soldier from his post and probably murder him . . . I immediately sent a non-commissioned officer and 12 men to protect both the sentry and the king's money, and very soon followed myself to prevent, if possible, all disorder . . . They soon rushed through the people, and by charging their bayonets in half-circles, kept them at a little distance. . . . The mob still increased and were more outrageous, striking their clubs or bludgeons one against another, and calling out, “come on you rascals, you bloody backs, you lobster scoundrels, fire if you dare, G-d d*** you, fire and be d***ed, we know you dare not,” and much more such language was used. At this time I was between the soldiers and the mob, parleying with, and endeavoring all in my power to persuade them to retire peaceably, but to no purpose. . . .
The whole of this melancholy affair was transacted in almost 20 minutes. On my asking the soldiers why they fired without orders, they said they heard the word fire and supposed it came from me. This might be the case as many of the mob called out fire, fire, but I assured the men that I gave no such order; that my words were, don't fire, stop your firing. In short, it was scarcely possible for the soldiers to know who said fire, or don't fire, or stop your firing.
What is the main idea or topic being expressed?