Defendant Michael Dunn reacts on the stand during testimony in his own defence during his murder trial at the Duval County Courthouse, in Jacksonville, Florida. Picture: Bob Mack

Jacksonville - A middle-aged software engineer opened fire on a black teenager because he felt disrespected when the 17-year-old refused to turn down the rap music blaring from his car, a prosecutor told a Florida jury in closing arguments on Wednesday.

Defence attorneys countered, saying Michael Dunn, 47, who is white, acted in self-defence when he shot Jordan Davis and was justified in using deadly force.

The trial, which has drawn international attention because of racial overtones and claims of self-defence, was put in the hands of a jury on Wednesday.

Davis was out on the town with friends when the argument broke out. Prosecutors said Davis used foul language when confronting Dunn, but that he was unarmed and never posed a physical threat.

“Jordan Davis didn't have a weapon. He had a big mouth. That man wasn't going to stand for it, and it cost Jordan Davis his life,” Assistant State Attorney John Guy said, wrapping up the prosecution's case at the end of a week-long trial.

“This case is not about self-defence. It's about self-denial,” he added.

The case has drawn comparisons to the trial of George Zimmerman, the former central Florida neighbourhood watchman who was acquitted last year of murder after saying he shot a 17-year-old unarmed black teenager, Trayvon Martin, in self-defence during a struggle.

Dunn is charged with first-degree murder in the November 2012 shooting of Jordan Davis. Dunn also faces three charges of attempted murder for firing 10 shots at four teens in the SUV parked in a Jacksonville gas station.

Prosecutors said Dunn overreacted in anger when Davis hurled expletives at him and refused to lower the volume.

“This defendant was disrespected by a 17-year-old teenager. He was not happy with his (Davis's) response,” said another Assistant State Attorney Erin Wolfson who delivered the closing argument.

She quoted a witness who overheard Dunn say: “You are not going to talk to me that way” as the altercation escalated.

Then Dunn “took it upon himself to silence Jordan Davis forever”, Wolfson said.

If found guilty, Dunn faces up to life in prison. Prosecutors say they will not seek the death penalty.

The verdict in the case remains in doubt, CNN legal analyst Sunny Hostin, a former assistant US attorney, tweeted on Tuesday night. “Especially in Florida, given the breadth of the stand your ground law and self-defence culture,” she said.

Deliberating the case is a jury of eight whites, two blacks, one Asian and one Hispanic.

Dunn's attorney, Cory Strolla, said the state had failed to prove its case, pointing to a lack of conclusive forensic evidence about where Davis was when he was shot.

“Michael Dunn was in a place where he had a right to be, asking for a common courtesy. He had no duty to retreat. He had a right to meet force with force, including deadly force,” said Strolla. “He's had that gun for 20 years and he has never fired it once.”

Dunn took the stand in his own defence on Tuesday and told the jury he started shooting in a state of panic after the exchange of words grew more heated and he thought he saw the barrel of a gun in the back window as Davis started to get out of the car.

Police said they found no weapon in the teens' SUV after the shooting.

“Michael Dunn doesn't get to just assume Jordan Davis had a gun and... was going to shoot him,” said Wolfson. “Self-defence does not let you assume.”

The prosecution sought to expose inconsistencies in Dunn's version of the incident.

The jury was reminded of dramatic testimony by Dunn's fiancée, Rhonda Rouer, who told the court that after the shooting Dunn never mentioned seeing a gun in the teens' car.

Medical evidence presented in court also showed that Davis died inside the car in a defensive posture.

Dunn's description of some of the expletives used in the altercation varied in court from a previous recorded account he gave to police.

In his closing argument, Strolla said the teens could have disposed of a weapon after they left the fuel station.

To illustrate his point, Strolla stood mute in front of the jury for three minutes, the time the Durango was gone before returning to the fuel station to get help.

Strolla criticised investigators for failing to secure the entire fuel station plaza as a crime scene or search for a weapon that night.

“They knew they messed up,” Strolla said. - Reuters