Evidence used in the Salem, Massachusetts witch trials of the 1690s was primarily “spectral evidence,” which referred to sightings of supernatural beings that had assumed human form. Such evidence was provided as testimony by individuals who accused others of witchcraft. These individuals testified that they had seen the accused inflict harm on others, usually without physically touching them. Those actions were interpreted as indicating that the accused was possessed by the devil or evil spirits functioning on his behalf.
To the accuser, the devil or spirit would not have been visible. Therefore, they could testify only to what they had seen the accused doing. Anyone who admitted to having seen the devil in nonhuman or nonanimal form could themselves be suspected of being a witch. Examples of the suspicious actions referenced in actual testimony include superhuman feats of strength and acts of mischief that followed outbursts of anger.
The authorities admitted the possibility that the accuser might have misinterpreted what they saw, which would result in accusing an innocent person. Because of the heavy reliance on spectral evidence and the possibility of error, the authorities strongly encouraged the accused to confess.