Editor's note: Carol Anderson is associate professor of African American Studies and History at Emory University and a public voices fellow with the Op-Ed Project. She is the author of "Eyes off the Prize: The United Nations and the African American Struggle for Human Rights" (Cambridge, 2003).
(CNN) -- In "Stand Your Ground" Florida, Michael Dunn said he felt threatened by a car full of teens playing loud music and pumped about 10 rounds from his 9 mm pistol into their SUV, killing 17-year-old Jordan Davis. There were, of course, no return shots, because the teens were unarmed. Dunn is white, and all the teens in the car were black. He didn't bother to call the police afterward.
Dunn, 47, is on trial, charged with murder.
He took the stand Monday, detailing how he was pulled up at a gas station when he asked the teens to turn down the music -- "rap crap" he called it. Through the teenagers' tinted windows he saw menace, someone reaching for something.
"You're not going to kill me, you son of a b***h," Dunn recalled saying as he reached for his loaded gun in his glove box. And he only "stopped firing when it appeared the threat was over."
Under Florida's "Stand Your Ground" law, which could be used in this case, you are granted immunity from criminal and civil charges -- even if you didn't first try to retreat -- if you can show you had a reasonable fear of imminent bodily harm or death. And reasonable is up to interpretation.
A 2012 study by The Urban Institute found that in the "Stand Your Ground" states, when white shooters kill black people, "34% of the resulting homicides are deemed justifiable. Only 3% of deaths are ruled justifiable when the shooter is black and the victim is white." And Dunn feels justified.
"I am NOT a murderer," Dunn has said. Instead, he has taken on the mantle of victimhood and claimed, "I am a survivor."
Dunn saw black and Dunn saw "threat." And he still does.
He wrote, while awaiting trial, "This jail is full of blacks, and they all act like thugs. ... This may sound a bit radical, but if more people would arm themselves and kill these **** idiots when they're threatening you, eventually they may take the hint and change their behavior."
But it's not just the vigilantes. In January, Philadelphia police determined that a group of African American teens wearing hats and scarves in 13 degree weather looked "suspicious." The resulting stop and frisk led to the crushed testicles of a straight-A student who was simply on his way to a high school basketball game. He is now in a wheelchair.
Recently, researchers at Stanford University conducted studies where police and others, cued with an image of a black person, quickly deciphered very blurred images often associated with crime, such as a gun. White people see an African American, and they're immediately looking for something illegal. They almost instantly see a threat.
Still, there's another story. The toll that the assumption of white innocence has on public safety is rarely examined.
For example, years ago in Wisconsin, one of Jeffrey Dahmer's young victims ran naked, bleeding and screaming into the arms of Milwaukee's finest. But the serial killer's blond hair worked like pixie dust: The officers ignored the pleas of several African American women, who begged the police to protect the child and get him to safety. Instead, the cops took Dahmer's word that this frail 14-year-old Asian American boy was really a consenting adult and handed the child back over to the cannibal.
For most Americans, danger doesn't look like Jeffrey Dahmer. The second part of the same study at Stanford affirmed it.
Researchers found when they flashed pictures of whites to police and others, subsequent fuzzy images linked to crime remained a blur for a lot longer. In the Rorschach psyche of America, the words "white" and "crime" are not synonymous.
This means that authorities are slow to recognize the threat even of serial killers and certainly by gun-toting shooters in neighborhoods, malls, schools, and airports -- if they're white.
The ability of white skin to mask a threat was evident in Atlanta last year. In October, a white man pulled up to an elementary school and breezed through an elaborate security system while packing multiple guns, including an AK-47, and nearly 500 rounds of ammunition. Eight hundred children scrambled out of the building and a SWAT team set up outside. Then, Michael Brandon Hill pointed his gun out the school window and started shooting.
As dramatic as the shootings may be, the assumption of white innocence has a more widespread, corrosive effect on the criminal justice system and society. The New York Police Department has documented evidence that the relatively small number of whites who were stopped and frisked accounted for nearly twice as many illegal firearms and one-third more contraband than blacks or Latinos.
Still, Deputy Inspector Christopher McCormick instructed his officers to target African Americans. "I don't have any trouble telling you this," he said, "male blacks 14 to 20, 21." In other words, where the presumption of white innocence is concerned, facts carry much less weight than perception.
Similarly, whites and Hispanics are two-thirds of all crack users in the United States; yet, the U.S. Sentencing Commission found that 79% of sentenced crack offenders in 2009 were black. As journalist Saki Knafo noted, "When it comes to illegal drug use, white America does the crime, black America gets the time."
Law professor Jonathan Simon wrote about the ways that the American obsession with crime has created "a culture of fear." Yet, any sense of real safety and security will continue to elude this nation as long black is the default threat setting in America.
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The opinions expressed in this commentary are solely those of Carol Anderson.