JACKSONVILLE (REUTERS) - Three days after a Florida jury found Mr George Zimmerman not guilty for the shooting death of Mr Trayvon Martin, the Reverend Jesse Jackson visited Jacksonville to call attention to another self-defence case that he called a "travesty" of justice.

Rev Jackson spent an hour in a jailhouse visit with Marissa Alexander, 32, an African American who was sentenced to a mandatory 20 years in prison for firing a warning shot into the wall of her home in 2010 to end a violent argument with her abusive husband.

"In one case Mr Zimmerman kills a young man and walks away, free to kill again," Rev Jackson said. "And Marissa shot no one, hurt no one, and she's in jail for 20 years."

Rev Jackson said the contrast in the Zimmerman and Alexander cases exposed injustices in the justice system.

"We see radical racial polarisation in the judicial system," Rev Jackson told the Florida Times-Union. "That's a cause of great concern."

After meeting with Alexander, Rev Jackson spoke with Ms Angela Corey, the state prosecutor who handled both the Martin and the Alexander cases. Ms Corey told him that Alexander's case is in the appeal phase and out of her jurisdiction, but Rev Jackson said he asked her to use her power to see that Alexander is released.

"Ours was a moral appeal," he said. "This mother has three children. They need their mother," he said, noting that Alexander had already served the three years originally offered to her by the state in a plea deal.

Mr Michael Dowd, a New York domestic violence attorney handling Alexander's appeal, contends she should not have been charged with felonies, but rather a misdemeanor, such as unlawful discharge of a gun.

Local leaders from the National Association for the Advancement of Colored People, the Southern Christian Leadership Conference and the National Action Network are calling for Florida Governor Rick Scott to pardon Alexander.

When Mr Scott appointed Ms Corey special prosecutor in the Zimmerman case and she brought second-degree murder charges against him, some legal experts said she had overcharged. After her office lost the case, many legal experts said prosecutors didn't have enough evidence to win a second degree murder conviction.

When Ms Corey first ran for office in 2008, the tough-on-crime Republican prosecutor promised voters she would pursue criminals to the fullest extent of the law.

Ms Corey also garnered national condemnation when she charged 12-year-old Cristian Fernandez with first degree murder in the death of his two-year-old stepbrother. At the time, Fernandez faced mandatory life in prison if found guilty.

In the Alexander case, Ms Cory charged the 32-year-old woman with three counts of aggravated assault with a deadly weapon because her husband's two children were in the house during the argument.

Alexander's case received little attention when she was convicted, but that changed after the Trayvon Martin killing cast a new spotlight on Florida's "Stand Your Ground" self-defence laws.

Under the "Stand Your Ground" law, people fearing for their lives can use deadly force without having to retreat from a confrontation, even when it is possible.

Alexander, a slightly built woman, said her husband, Rico Gray, was moving towards her threateningly when she fired into a kitchen wall. He had previously been convicted on a domestic violence charge for attacking her.

Mr Gray's two children were at home, in the living room.

Prosecutors alleged that the shot endangered Mr Gray and the children.

Alexander filed a "Stand Your Ground" claim, but a judge ruled against her because Alexander chose to go back into the house with her gun.

A jury took just 12 minutes to find her guilty of three counts of aggravated assault with a deadly weapon.

Because Alexander fired a gun in the incident, Florida's "10-20-Life" mandatory-minimum sentencing guidelines required the judge to sentence her to 20 years in prison.

At the time, Alexander had an active restraining order against her husband and she carried a concealed weapons permit.