The fourth mass trial at Chelmsford took place in 1645, the worst witch trial of the seventeenth century, when, of thirty-two women indicted, nineteen were hanged. This was mostly due to the efforts of Matthew Hopkins, a witch hunter, who, "in fourteen months' time sent to the gallows more witches than all the other witch hunters of England." Most of the Chelmsford witches made confessions; this is not strange, for Hopkins and his associated developed techniques to secure whatever confessions they needed. All at once, enthusiasm and backing for Hopkins disappeared. People began to suspect his integrity especially regarding his fees; judges asked him about the way he tortured women for their confession.

Public sentiment about Matthew Hopkins is clearly visible in Samuel Butler's 1664 poem Hudibras:

And has not he, within a year,
Hanged three score of them in one shire?
Some only for not being drowned;
And some for sitting above ground'Whole nights and days upon their breeches,
And feeling pain, were hanged for witches;
And some for putting knavish tricks
Upon green geese and turkey chicks,
Or pigs that suddenly deceased
Of griefs unnatural, as he guess.

King James I in 1604 imposed severe penalties for witchcraft. His edict developed the idea that a witch knowingly formed a pact or covenant with the Devil. It became a felony to covenant with any evil or wicked spirit. This covenant was the core of the witchcraft delusion, although many indictments still charged a witch with simple acts of maleficia (general evil-doing).