The pawnbroker is an unattrative and unpleasant woman who is perceived by him as being rude. He visits the pawnshop 1)to pawn his watch, and 2)to make plans for robbing the pawnshop. He knows she keeps the pawned items she takes in in a trunk in the back room of the shop, and he knows she wears the keys around her neck. He kills her because he wants to rob her, and he kills her sister because she comes home during the crime.
Raskolnikov believed that he was a "super-human," that he could justifiably perform what society considered a despicable act—the killing of the pawn broker—if it led to his being able to do more good through the act. Throughout the book there are examples: he mentions Napoleon many times, thinking that for all the blood he spilled, he did good. Raskolnikov believed that he could transcend this moral boundary by killing the money lender, gaining her money, and using it to do good. He argued that had Isaac Newton or Johannes Kepler had to kill one or even a hundred men in order to enlighten humanity with their laws and ideas, it would be worth it. Thus he is thrown into a moral existential confusion over the death of the pawnbroker's sister. Never at any time in the novel is he repentant over the death of the pawnbroker.