I have an idea for a thriller about a high school girl who becomes very lonely because she cannot get any guys and is a target for bullying or just not popular. Her loneliness and angst towards the opposite sex causes her to go crazy and take desperate measures., including murder. She is the antagonist though and the police detective, investigating the case, is the protagonist and it's told from his point of view for most of it. Halfway through the story, she ends up killing a close friend of the cop's and he wants revenge, and comes up with scheme, using her own weaknesses against her, to get it. However, before this happens and he has no reason to get revenge for the first half, I am not sure what approach to take to make this protagonist interesting. He should probably have a psychological and/or moral flaw that is within similar theme's to the villains, but does anybody have any ideas as to what that could be? Or some sort of personal drive or goal. How I can make him compelling for the first half, rather than just another run of the mill cop, assigned to a case?