Kerby was one of two men, the other surnamed Roger, who stood accused under the terms of the Act of Six Articles of not accepting the doctrine of transubstantiation.
Their gaoler was John Bird, a sympathetic man who had already run close to implication under similar charges, and was much later actually accused by the Commissioners.
An important figure instrumental in the accusation against Kerby and Roger was one William Foster, a Justice living at Copdock (a little south of Ipswich), who was later very active in the arrests of the martyrs Rowland Taylor, Robert Samuel, Agnes Potten and Joan Trunchfield.
The night before, a bill was nailed to the door by an unknown person, carrying the following words: Juste judicate filii hominum: Yet, when ye shall judge, minister your justice with mercy.
Beware of innocent blood-shedding; take heed of justice ignorantly administered; work discreetly as the Scripture doth command; look to it that ye make not the Truth to be forsaken.
The Justices assembled in the Town Hall, and the prisoners were brought in, who 'made their prayers secretly to God for a space of time' with eyes and hands lifted up to heaven.
Lord Wentworth pronounced the sentence of death upon them, at which Kerby held up his hands and, bowing devoutly with humble reverence, he said "Praised be Almighty God," and then stood there amid a profound silence.
A large crowd (many hundreds) of the public gathered on the Saturday to witness the execution, which was held at the Cornhill (then called the Market Place) outside the Town Hall.
Adjacent was the market building called the 'Shambles', a large timbered structure with an arcade around the ground floor, and with a balcony above from which public spectacles could be viewed.
A large company, including most of the neighbouring justices, were assembled there, and the stake, broom and brushwood faggots were set up in the centre of the Cornhill.
The flames were kindled, and with a loud cry to God Kerby beat upon his breast 'so long as his remembrance would serve'; and, in the words of a modern writer, 'in a chariot of fire his soul passes into the unseen world.'