The investigators most likely ascribe to James's Peripheral theory of emotion.
James's Peripheral theory of emotion also called the James Lange theory of emotion developed by 19th-century scholars, William James and Carl Lange explains that individuals experience emotion as a feeling of physiological changes due to a stimulus such as fear; guilt; etc.
The investigators hope that through the physiological changes occurring during investigation, they can be able to conclude exactly what J T feels(emotions) and draw conclusion as to whether he committed the crime or not.