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George Zimmerman, a 28-year-old neighbourhood watch volunteer in Florida, has admitted to shooting and killing 17-year-old Trayvon Martin, who was unarmed and walking home from a store.

But police never arrested Zimmerman, saying there was no way to prove he hadn't acted in self-defence, as he claimed.

Martin's family says Zimmerman's claim is nonsense. Martin was carrying nothing but a bag of candy, they said, and a friend who was on the phone with Martin at the time said he was frightened by Zimmerman, who was following him.

The case has led to accusations of racial profiling against Zimmerman and now involves federal prosecutors and civil rights groups from across the nation.

Al Jazeera's Andy Gallagher reports from Miami.

Source: Aljazeera