A man who claims he killed his wife in self-defence, before posting a photo of her dead body on Facebook, fatally shot her because she threatened to leave him, a court has heard.

Derek Medina shot 27-year-old Jennifer Alfonso eight times during an argument in their home, Florida prosecutor Leah Klein said in her opening statement on Tuesday.

Medina was an undefeated amateur boxer who "had nothing to fear" from his 5ft 6in wife and would never let her leave him, Ms Klein told the court.

"He never lost a fight. He wasn't going to lose to his wife," she said. "He wasn't going to lose by letting her leave as she said she was going to do."

Medina, 33, who claims he acted in self-defence, admitted to the August 2013 killing in posts on Facebook.

"I'm going to prison or death sentence for killing my wife love you guys miss you guys take care Facebook people you will see me in the news," he wrote.

Picture: This image taken from the Facebook page identified as Derek Medina's shows a post that appeared on the page preceding a separate post that included a photo of his dead wife, Jennifer Alfonso.  (AP Photo)

The next and final post, called "Rip Jennifer Alfonso", was a gruesome photograph showing a woman in a black leotard slumped on the floor.

The photo was up for more than five hours before Facebook removed the page.

Ms Klein told jurors on Tuesday the post was Medina's way of claiming a victory.

She said: "He did what people do when they win. He did what was good for him."

Medina's defence, who deferred making an opening statement, contend Ms Alfonso abused drugs, battered her husband and was involved in Satan worship.

One of the trial's first witnesses was a work colleague of Medina's who testified the accused mentioned to him that Ms Alfonso had been punching him.

"He said there was years of abuse and he wasn't going to take it anymore. He said she was punching him," Paul Ampudia told jurors.

Court records indicate the couple had a tumultuous relationship. They were first married in January 2010, divorced in February 2012 and then remarried three months later.

Authorities said the argument that led to the shooting began in the couple's bedroom, where Medina allegedly threatened his wife with a gun when she threw mascara and towels at him.

The heated exchanged continued in the kitchen, where Medina told police he was threatened with a knife. He then went back upstairs for his gun before the fatal shooting occurred.

Medina faces life in prison if convicted. He is also charged with child neglect because his wife's 10-year-old daughter was in the home at the time of the killing.