Once Chillingworth decides to pursue Hester's lover and enact revenge, he pursues this purpose with the techniques and motives of a scientist. Moving in with Dimmesdale he pokes and prods. His hypothesis is that corruption of the body leads to corruption of the soul. "Wherever there is a heart and an intellect, the diseases of the physical frame are tinged with the peculiarities of these [the intellectual thoughts]." In Chapter 9, "The Leech," Chillingworth's motives and techniques are explored. As a scientific investigator, he cold-heartedly and intellectually pursues his lab specimen. Hawthorne says, "Few secrets can escape an investigator, who has opportunity and license to undertake such a quest, and skill to follow it up."
When Chillingworth begins his investigation, he does so as a scientist. Hawthorne writes, "He had begun an investigation, as he imagined, with the severe and equal integrity of a judge, desirous only of truth, even as if the question involved no more than the air-drawn lines and figures of a geometrical problem, instead of human passions, and wrongs inflicted on itself." Here the cold intellect of the publicly emerging nineteenth century scientist is used as a framework for Chillingworth's pursuit. This is what makes Chillingworth diabolical and, in Hawthorne's eyes, the greatest sinner. He violates Dimmesdale's heart and soul to see how he will react. Of human compassion, he has none. Eventually when Hester talks with him about whether Dimmesdale's debt has been paid, Chillingworth says that it would have been better had he died than endure seven years of vengeance.
