I'm thinking INTP. He is definitely a Ne/Si type. He frequently uses Ne by imagining various possible outcomes of hypothetical situations, and Si by observing patterns in the behavior of killers and being able to identify them using these observations (profiling). He doesn't seem to have much Se at all (he is completely uninterested in sex, alcohol, etc. and does not exactly "live in the moment"). His Ni seems low as he lacks the instinct to stay away from potentially dangerous people when everyone around him can sense when something is off. He allows himself to be manipulated by Lila, then befriends Miguel Prado only a few episodes later.
Dexter seems to lead with Ti, as he values logic above all else. He doesn't lead with his emotions and he doesn't cut corners to get what he wants. Although he does not connect emotionally with others, he easily picks up in social norms, which us a sign of inferior Fe.
When Dexter is stressed, angry, or panicking, he starts using Fi, which is most likely a shadow function. In this mode, he makes impulsive decisions that reflect what he wants to do, disregarding any sort of reason. This seems to be an attempt to rebel against the life his father has planned out for him, which is another sign of Fi use. I don't see a lot of shadow Te, mostly just Fi, but it's enough to convince me that it is not in his function stack.
So yes, INTP.