Abstract: Guilty knowledge or malicious intent can be identified in a subject by presenting a stimulus to the subject, detecting an electrical potential at a location on the skin of the subject, detecting infrared light reflected from the brain of the subject, and analyzing the detected electrical potential and the detected infrared light to identify an indication of guilty knowledge or malicious intent. Also, an identified indication of guilty knowledge or malicious intent can be associated with the presented stimulus. Guilty knowledge or malicious intent further can be identified by detecting one or more muscle movements comprising a facial expression and analyzing the one or more detected muscle movements to identify a visible indication of guilty knowledge or malicious intent, which also can be associated with the presented stimulus. Additionally, the stimulus can comprise one or more of a question, an image, a video clip, a sound, and an audio clip.