When reports of witchcraft began circulating in Essex County, Corwin was one of the magistrates called on to make preliminary inquiries into the reports. He and John Hathorne, another local magistrate, held hearings in early March 1692 in which testimony was gathered from Tituba, Sarah Good, and Sarah Osborne, the first three women accused of being witches. Due to the uncertain constitutionality of the Massachusetts government in 1692 (its charter was vacated in 1684, and it had reformed with the charter following the 1689 Boston revolt that ended Dominion rule of Sir Edmund Andros), there was a reluctance among colonial leaders to establish courts to hear the cases until Sir William Phips arrived in May 1692 with the charter that established the Province of Massachusetts Bay.