On the night of March 5, 1770, a party of British soldiers shot and killed five Bostonians in an event known ever since as the Boston Massacre. The killings shook the loyalty of Britain’s North American colonists to the British government. John Adams wrote that the “foundation of American independence was laid” that night. The basic outline of what happened is well established, although the fine details are elusive. The soldiers who participated in the killings were tried for murder, and dozens of eyewitness accounts were entered into...