Where they say they don't think he's a murderer because I think the angle of the wound was wrong since he's right handed or something? So they go exploring the amusement park and meet a bum who says it was the main character who murdered the person after all. So they go home and the main character is texting his female friend about meeting up with his sister or something, but then the female friend from school tells him he doesn't have a sister. So he thinks his sister is the murderer because she's left-handed and has a scalpel (since she's a nurse or something).

I forget what else happens aside from the main character spazzing out over hallucinating about the bum and some pictures with the bum in them somehow... but in the end it turns out the female friend was the murderer after all because she'd been on a date with the main character and then some dude tried to rape her. She killed him and when the main character first found her immediately post-murder, he decided to take the blame because he loves her or something. He left a note to his future memory-less self by stitching up a wound with a piece of paper inside that said "Take care of her". However the girl didn't want to get caught so when they went snooping around in the amusement park with their friends, she'd gotten the bum to agree (by using her body) to accuse the main character when he came by again. In the end she get arrested after killing the bum...