MIAMI — For decades Florida has had a history of deadly, racially tinged police confrontations, many of them involving unarmed men, which have led to riots, protests and a steady undercurrent of rancor between minorities and the police. But in the past 20 years, not a single officer in Florida has been charged with using deadly force.

As a grand jury considers the case of Darren Wilson, the officer who shot and killed Michael Brown on Aug. 9 in Ferguson, Mo., Florida’s experience points to both local and national factors making it extraordinarily difficult to prosecute, let alone convict, law enforcement officials for killing someone in the line of duty. Police officers have the authority to use lethal force if they believe they or others are in danger. More often than not, across the country, that right is one of the factors that make hurdling “beyond a reasonable doubt” a challenging task, prosecutors and defense lawyers said.

In Florida, even getting a decision on whether to seek charges is problematic. Three years after a particularly notorious episode in South Beach, a 2011 Memorial Day weekend shooting in which a 22-year-old was killed when the police fired more than 110 bullets at his car after it had stopped, prosecutors have still not decided whether to bring charges against any of the 12 officers, despite pressure to do so. Four bystanders were also wounded during the barrage. The shooting is one of 42 cases involving lethal use of force by the police, some dating back several years, now being reviewed by the Miami-Dade Office of the State Attorney.

Prosecutors and defense lawyers agree that the system is intended to protect police officers and give them the benefit of the doubt, though they can differ sharply on where they think the lines should be drawn.