Inside the courthouse in Jacksonville, Fla., the murder trial of Michael Dunn, a white computer programmer accused of shooting a 17-year-old black youth after an argument over loud rap music, was winding down Wednesday, with closing arguments under way. Meanwhile, those following the case from the outside were hotly debating the meaning of online commentary, ostensibly written by Mr. Dunn, in which the author blames “thug culture” for the shooting.

The written commentary, which states that the black teenager and his friends brought the tragedy on themselves by adhering to a "thug culture" that glorifies violence, was not presented to jurors who will soon be considering Dunn's fate. (Dunn did mention the website, justicefordunn.com, when he took the stand Tuesday to testify in his own defense.) But its message is stirring anew concerns about the explosive mixture of looser gun laws and individuals' own biases toward people different from themselves, as well as, on the other side, backing from those who applaud people willing to try to enforce what they see as the social order.

Dunn, who is on trial for first-degree murder and attempted murder, testified Tuesday that the November 2012 incident began with his request to turn down the music pulsing from the vehicle of a group of black teens. As he argued with them in front of a convenience store, the argument escalated into a "life or death" situation, said the 47-year-old Dunn. He testified that he saw a weapon, whereupon he fired nine times into the men's SUV, killing teenager Jordan Davis. Police found no weapon.

On the justicefordunn website, set up by Dunn's family, a more contextual defense appears. “I blame ‘Gangsta Rap’ music and the thug culture that goes along with it for influencing violence,” an author purported to be Dunn writes.

The Michael Dunn-Jordan Davis case is in the media spotlight in part because it carries some of the same racial overtones as did the fatal shooting of teenager Trayvon Martin in early 2012. Trayvon, who was African-American and unarmed, was shot to death by George Zimmerman, who is white and Hispanic, after the two tussled in a Sanford, Fla., neighborhood. Both Zimmerman and Dunn say they acted in self-defense.

The case also coincides with an ongoing national debate over the liberalization of concealed weapons laws and a new breed of self-defense laws. And, though the jury didn't hear much of it, the Dunn family website would indicate that coded language surrounding race is part of the equation. Dunn's girlfriend, in her testimony about what happened, referred to Dunn's complaint about "thug music," and on Wednesday prosecutor John Guy pointed jurors to Dunn's use of the word "gangsters" to describe the teenagers.

“Our historical moment is one in which, on one hand, we’re no longer allowed to talk in openly racist terms, so we’re resorting to coded language like ‘thug’ or ‘gangster,’ ” says George Ciccariello-Maher, a political scientist at Drexel University, in Philadelphia. “But that’s not all of it. We’re also in a period of what you could call aggrieved whiteness, where white people increasingly feel they are victims of racism.

“In the case of Michael Dunn, he’s both of these things at once: He is clearly coding race through this term ‘thug,’ but then also is perfectly capable of feeling like he’s the victim of this loud music,” he says.

Despite the judge's efforts to keep it out of the trial, race has become more pronounced in the Dunn case than it was in the Zimmerman trial, given Dunn's apparent views on black culture. (Though prosecutors argued that Mr. Zimmerman had profiled Trayvon because of his appearance, Zimmerman said through proxies that he had no problem with black people in general.)

The justicefordunn website, referring to the sequence of events that led Dunn to fire on the SUV, poses this question: “Should you be afraid?”

“Google ‘black on white murders’ and check out the results,” the website reads. “There are 4,270,000 results … – there’s a whole lot [of people] that have lost their lives because they were un-armed and unable to defend themselves when their lives were threatened.”

In a forum called “Michael’s Comments,” the author defends states' “stand your ground” laws that deepen legal protections for shooters who claim self-defense, and writes, “I am not a murderer, I am a survivor.”

The writer then blames Jordan's death on the “violent sub-cultures that so many young men become enthralled with [and which] are destroying an entire generation. Root cause analysis says to correct the behavior. The black community needs to do a better job of selling worthwhile role models.”

The comments jibe with sentiment expressed in letters released by the state of Florida, written by Dunn from his jail cell while awaiting trial. In one to his daughter, Dunn writes: "This may sound a bit radical but if more people would arm themselves and kill these [expletive] idiots when they're threatening you, eventually they may take the hint and change their behavior.” Those letters were not submitted as evidence in court.

In the trial itself, Dunn’s defense lawyers posited that the group of young black men ditched the firearm before police arrived. Prosecutors say police found no weapon because there never was a weapon.

Dunn's defense team is asserting justifiable use of a weapon in self-defense. In his testimony, Dunn said that Jordan reached down and picked up something that resembled a shotgun – four inches of which he saw through the car window – as the argument over the music escalated.

"He’s showing me a gun and he’s threatening me," Dunn, who has a permit to carry a concealed weapon, told the jury. "I was in fear for my life and I was probably stunned…. I had never been threatened, let alone with a firearm before…. I couldn’t believe what I was seeing and hearing." He added: "This is the point where my death is imminent. He's coming to kill me. He's coming to beat me."

That testimony should be enough to acquit Dunn because he "had the right to meet force with force," defense attorney Cory Strolla argued on Wednesday in his closing argument. "He is innocent – innocent – not even not guilty."

Prosecutors, in their closing arguments, argued that the evidence shows premeditation. Dunn calmly and systematically shot at an SUV full of people as the vehicle peeled away to get out of danger, they said. Dunn fired 10 shots: Nine hit the SUV, and three hit the back of the vehicle as it sped off. Jordan Davis was bent over toward the SUV floor when he was fatally hit, according to testimony.

“This defendant, when he pulled up next to that SUV, his blood started to boil," prosecutor Erin Wolfson said in her closing argument. "He didn’t like the music that was coming out of the car next to him. He got angrier and angrier as that music irritated him. This defendant went crazy. He got angry at the fact that a 17-year-old kid decided not to listen to him.... When he pulled out his gun, he shot to kill."

After the jury gets the case, the 12 jurors will have to deal with facts that point to Dunn as the aggressor. But jurors may also wrestle with the deeper cultural perceptions of young black men that Dunn details on his website, says Mr. Ciccariello-Maher at Drexel.

The law “in this case doesn’t justify [someone] being the aggressor and firing into a fleeing car,” he says in a phone interview. “But Dunn may get off if he convinces the jury that [he was] sufficiently threatened. The question for the jury is: Do you trust this man, or do you trust these scary-looking youths?”