ORLANDO, Fla. (AP) - The parents of a black teenager fatally shot by a white neighborhood watch volunteer want the FBI to take over the investigation.

The parents of Trayvon Martin told an Orlando, Fla., press conference Friday they no longer trust the Sanford Police Department. Their 17-year-old son was fatally shot last month as he returned to a house in a Sanford neighborhood during a visit from Miami.

Sgt. David Morgenstern says the department stands behind its investigation but welcomes another agency "to scrutinize and review" the case.

George Zimmerman told police he shot Martin in self-defense. Zimmerman called 911 to report a suspicious person. He was told to stay in his car and an officer would be there shortly. But Zimmerman exited his car, fought with Martin and eventually shot him. Martin was unarmed. Zimmerman hasn't been arrested.