Falso suicidio

Urban Legend has it that if you kill your college roomate, you get a 4.0 for the semester. So when Chris goes along with Tim pushing Rand off the curve, they have good reasoning for it. Besides, Rand is always being a jerk to his girlfriend Natalie who is Emma's roomate. After his girlfriend Natalie finds out about his death, she kills herself by jumping off the curve. Later Chris's girlfriend Emma tries to convince him that Tim is setting him up for the murder and trying to seduce her. Then suddenly Chris's girlfriend is taking a 4.0. Is Emma behind this too, is Rand really dead, and does Chris have something planned for Tim? If so why everyone is playing with each others head?