During the trial of Servetus, Bullinger was kept informed of things by his friend Haller. In a letter dated 27 September, 1553 Haller writes
Yesterday we received the documents in the case of Servetus, and have since been studying them in view of our reply. But we should like to know what your answer is before we send ours. We therefore entreat you immediately to inform us of its tenor. Yet wherefore so much ado! the man is a heretic, and the Church must get rid of him. Let me, however, I beseech you, speedily know the conclusion you have come to.
R. Willis remarks
The Zürich pastor would seem to have been the most active of all the ministers in collecting and imparting information of a kind that would lead to unanimity of conclusion among the Churches and Councils. His friend, Ambrose Blaurer, acknowledging receipt of a letter from him communicating the decision of Zürich, says that he ‘had thought the pestilent Servetus, whose book he had read twenty years ago, must long since have been dead and buried.’ But the … man must add further: ‘We are surely tried by heresies and satanic abortions of the sort, in order that they who are steadfast in the faith may be made known.’*
*R. Willis, Servetus and Calvin: a study of an important epoch in the early history of the reformation, p. 460.