The parents of an unarmed teenage boy who was shot and killed in Sanford, Florida last month are now calling on the FBI to get involved in the investigation. Trayvon Martin's parents have formally asked the FBI to investigate this case, because they believe local police and prosecutors have not done their job. The admitted gunman remains free - and this case has growing overtones of race and injustice. Martin's parents say recently-released 911 calls prove the shooter, a neighborhood watch volunteer, was not acting in self-defense, as he has claimed.