By colonial history standards, the Salem Witch Trials are actually fairly well-documented. To make her argument in In the Devil's Snare, historian Mary Beth Norton uses many of the same primary sources that previous historians of the Trials used. Many of these documents were edited and published by historians Paul Boyer and Stephen Nissenbaum under the title The Salem Witchcraft Papers. Norton also draws heavily on the manuscript court papers found in the Essex County Court Archives.

The choice of sources is relevant to Norton's argument. Some other historians have used wills, probate records, and deeds to reveal the social undercurrents of the Witch trials—in particular the relative wealth of the accusers and the accused and the complex legal and social relations between them. Norton acknowledges these aspects of the crisis, but her argument hinges on a close reading of the court documents, especially depositions and examinations that reveal a great deal about the fears of the participants in the trials.

From these, she concludes that "the witchcraft crisis of 1692 can be comprehended only in the context of two decades of armed conflict between English settlers and the New England Indians." She finds that many of the accusers and the afflicted had experienced the violence of frontier war and sees in their descriptions of evil spirits and even Satan himself echoes of these horrors. Satan, she argues, is often portrayed in ways evoking radicalized concepts of Native Americans in the courtroom testimony and depositions of participants.

Norton also reads these court sources against private and public letters, sermons, and even publications (like the Reverend Cotton Mather's Wonders of the Invisible World and History of Remarkable Occurrences in the Long War) that help shed light on the ways that New Englanders imagined the spiritual world around them in light of the trauma of war. She argues that these sources reveal "the phenomenon known today as post-traumatic stress disorder" as a significant factor in the terror of the witch trials.

Significantly, though, Norton also makes inferences from sources that she believes have been deliberately destroyed by later generations, embarrassed by their ancestors' conduct in the hysteria. These include "extensive contemporary notes" kept by contemporary observers like the Reverend Samuel Parris and Judge Waitstill Winthrop. Anticipating scholarly criticism for this approach, Norton actually offers her explanation of this significant gap in the sources in the book's introduction.