Someone has stepped up, reporting to have witnessed last month's shooting of Trayvon Martin, an unarmed 17-year-old whose death has sparked nationwide controversy. The witness detailed to CNN the Florida incident from what initially sounded like an argument to its fatal conclusion. "It would have to be starting with hearing voices, but not seeing, and then, after the voices, opening a window and then seeing -- with two men or two people on the ground, one on top of each other," the witness, who...