Homework (2018)

Mike receives a text at while working on his homework. She flirts with him and invites him over. But he has a test. Later - He changes his mind, letting her know that he's on his way over. But she doesn't answer the texts, she doesn't answer the door either. He leaves in a huff. Inside Jackie's apartment a masked intruder watches her as she sleeps. He murders her in her bed. The killer takes her phone and texts Mike. It is at this moment that we realize, that Mike's text conversation was this killer the entire time.