You might want to consider the way that Porfiry Petrovich is used to comment upon the theme of guilt in Part IV, Chapter V when he talks to Raskolnikov whilst he goes to Porfiry's office to reclaim his belongings. Note what Porfiry says in this quote and how he refers to the implicit guilt of Raskolnikov and the psychological aspect of the crime:
What is it, to run away! A mere formality; that’s not the main thing; no, he won’t run away on me by a law of nature, even if he has somewhere to run to. Have you ever seen a moth near a candle? Well, so he’ll keep circling around me, circling around me, as around a candle; freedom will no longer be dear to him, he’ll fall to thinking, get entangled, he’ll tangle himself all up as in a net, he’ll worry himself to death! ...he’ll keep on making circles around me, narrowing the radius more and more, and—whop! He’ll fly right into my mouth, and I’ll swallow him, sir, and that will be most agreeable, heh, heh, heh!
The determined way that Porfiry declares that Raskolnikov will be unable to ignore the "law of nature" indicates the way that humans are unable to ignore their guilt, hinting very strongly that either Raskolnikov will either be driven into madness by his guilt or obliged to confess to the crime. The analogy that Porfiry draws between a criminal struggling with his guilt and a moth drawn to a candle makes the inevitable outcome of such a process: guilt is a moral force that cannot be denied or ignored, as Raskolnikov will come to discover.