At least 21 states (in blue) have laws allowing citizens to use deadly force without attempting to retreat when threatened outside the home.

By now, the scene is familiar: Two men get into an altercation — one black, one Hispanic. One is armed with a handgun and shoots the other dead.

The victim is unarmed; the shooter claims self-defense and walks free.

For more than a month, the victim's family waits to see whether authorities will file charges against the shooter.

Except this tragedy did not play out among the hedges of a Sanford, Fla. apartment complex, where a Hispanic neighborhood watch volunteer shot and killed an unarmed black teen. It occurred under the flourescent lights of a Taco Bell parking lot in Phoenix on April 3, when a black driver and an Hispanic pedestrian got into a shouting match and the driver shot the pedestrian dead.

As in the Trayvon Martin case in Florida, in which police did not arrest George Zimmerman for 45 days, a stand-your-ground law is influencing law enforcement action in the Phoenix shooting. Since Trayvon's death, these laws — and how they are applied by police and prosecutors — are under renewed scrutiny.

At least 21 states have adopted some variation of the controversial law that says a person does not have to retreat in the face of a threat and can use deadly force if they fear they are in danger of death or serious harm.

"I look at the Trayvon Martin case, and what happened to my son is almost the same thing," says Daniel Adkins, 59, who mourns the death of his only son and namesake, Daniel Jr., 29. "I want justice. … Why haven't they arrested him?"

Most stand-your-ground laws grant a person who uses deadly force the presumption that he acted reasonably unless there is evidence to the contrary.

If there are no witnesses and the victim is dead, or if the evidence is conflicting, the chances are greater that someone can "get away with murder," Savannah Law School professor Elizabeth Megale says.

"The statute can be used and distorted by hard-core criminals or someone who has committed a crime," she says. "Most times, someone will get arrested if the other person does not die. … It's ironic. If someone dies, the other person is less likely to get arrested."

John Roman, a fellow with the Justice Policy Center at the Urban Institute, analyzed homicides in the U.S. from 2005 to 2009. He found that homicides are twice as likely to be ruled justifiable in stand-your-ground states than in those without such laws.

The presumption that a person acted reasonably is appropriate, says Charles Heller, co-founder of Arizona Citizens Defense League, which advocates for gun rights.

"People have a right to defend themselves," he says. The presumption of reasonableness makes police and prosecutors think twice before charging someone. "It stops avaricious prosecutors from overdoing their jobs."

In Phoenix, family members of Daniel Adkins Jr. say they understand the frustration the Martin family felt when their son's killer was free.

But unlike the Martin case, where civil rights leaders pounded their pulpits and thousands protested and signed petitions calling for an arrest, the Adkins case has remained mostly below the radar.

"Why, with the police knowing what he did, is he still free? What are they waiting for?" Adkins' mother, Antonia, 63, asks in Spanish. "The law is the law, but it's an injustice."

After the nationwide protests, Zimmerman was arrested April 11 and charged with second-degree murder. Prosecutors say he racially profiled Trayvon. Zimmerman pleaded not guilty, saying he shot Trayvon in self-defense.

Adkins' parents say they don't believe their son's shooting was racially motivated.

Daniel Adkins Jr. was mentally disabled and lived with his parents. They say he was on his usual evening walk with their yellow Labrador, Lady.

About a mile from home, he walked in front of a silver Pontiac Grand Am in the parking lot of the Taco Bell, according to the police report of the shooting.

In the car was Cordell Jude, 22, and his girlfriend, who was eight months pregnant. Police have not publicly identified Jude, but he is named in the police report.

Jude had to brake fast in order to avoid hitting Adkins, he told police.

"Watch it!" he said Adkins yelled and added an obscenity. Adkins then moved to the driver's side door and swung an object that Jude describes in the police report as a bat or pipe. Jude's girlfriend also told police that Adkins swung what looked like a bat or a pipe . Nothing hit Jude or the car, the report says.

Jude then pulled his Smith and Wesson .40-caliber handgun from where he carried it — inside his sweatpants on his right hip, the police report says.

"Holding the gun in his right hand, with the barrel pointed toward Adkins, Jude racked the slide of the gun, loading a round into its chamber," the report says. "Jude stated that as Adkins raised an arm as if to swing at him again, Jude shot him once in the torso."

Adkins died, holding his dog's colorful green leash, in his right hand. The officers who responded to the scene found the dog still at his side. They did not find a pipe, bat or other weapon.

Jude said he didn't drive away from the confrontation because the dog was in the way. He told police he feared for his life and the lives of his girlfriend and their unborn baby. In response to a follow-up question by investigators, Jude said he did not think Adkins would have killed them, but he thought Adkins was trying to hurt him.

Jude did not return telephone calls for comment. A woman who answered the door at his suburban Phoenix home recently said Jude was not home and no one else in the family would comment.

The police report recommended second-degree murder charges against Jude. Police spokesman Sgt. Tommy Thompson would not discuss the case except to say the investigation continues.

Maricopa County Attorney spokesman Jerry Cobb also would not comment on details of the case. He says it will be reviewed by a committee of seasoned prosecutors that was set up two years ago to evaluate self-defense cases.

Roman, of the Urban Institute, says the Phoenix shooting is a prime example of the trouble with stand-your-ground laws. He says police can't arrest the shooter and question him in detail, even though interviews are critical in cases like this.

"It's another barrier to justice," he says.