Disclaimer: I do not own Pretty Little Liars!
He doesn't hesitate or back away quickly when he kisses you. He strides forward confidently, leans down, and captures your mouth with his. As you stand there, the thought occurs to you that your lips might be touching the ones that spoke the last words Ali ever heard. Your hands might be grasping the ones that held the weapon that caused her heart to stop beating.
But you don't believe it anymore. How could it be true? He was the boy who counteracted your impressive 'glyceraldehyde' with a simple 'goofball' while playing Scrabble. The boy who offered you his shirt to wear to bed after boldly asking "Top or bottom?" and then let you keep it the next morning. You'd felt safer during one night with him than you had your whole life at home. A killer wouldn't give you a sense of security, would he?
No, you are fairly certain now that Toby Cavanaugh and Alison's murderer are not the same person. He can't be guilty of ending her life. Instead, it seems that he has committed another crime. For in a single night, he has apparently stolen your heart. And you wouldn't really mind if he kept it.