In the play "The Crucible," the community puts men and women on trial for being witches. Unfortunately for these men and women, it was virtually impossible once accused to convince others of their innocence. If a person was accused of being a witch, that person had two choices: to admit to being a witch and accuse others of witchcraft, or to deny witchcraft and be executed. Therefore, the only real verdict could be a guilty one. Those who would not confess were killed, and those who did confess did so only to avoid execution.
The court of Salem ignores the "innocent until proven guilty" clause because those accused had no way to acquit themselves. Once accused, the person would be automatically considered guilty, and could only redeem themselves by accusing others of the same crime, setting off a vicious cycle of betrayal.