George Zimmerman, the Florida neighbourhood watchman who shot dead an unarmed black 17-year-old male last year, has been found not guilty. Lawyers for Mr Zimmerman, 29, argued he acted in self-defence and with justifiable use of deadly force in the death of Trayvon Martin. The jury retired on Friday to consider its verdict on charges of either second-degree murder or manslaughter. The case sparked a fierce debate about racial profiling in the US. Spontaneous protest marches were staged overnight in US cities including San Francisco, Philadelphia, Chicago, Washington and Atlanta, US media reported. Police and community leaders appealed for calm in Sanford, the Florida town where the shooting took place.