“We want justice, we want peace,” chanted dozens of students at Saginaw Valley State University, on their march to a nearby 7-Eleven Wednesday. Seventeen-year-old Trayvon Martin of Florida was shot to death on his way back from a snack run by neighborhood watch captain George Zimmerman. Zimmerman claimed self-defense, but police video obtained by ABC News Wednesday shows a cuffed Zimmerman without any visible signs of attack. He was questioned but not charged in Martin’s death.