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UPDATE 5/7 9:41 pm ET: Gregory McMichael, 64, and his son, Travis McMichael, 34, were arrested and charged with murder and aggravated assault, the Georgia Bureau of Investigation announced Thursday, just hours before what would have been Arbery’s 26th birthday.

After more than two months, Georgia still hasn’t brought charges against two white men who chased down Ahmaud Arbery, a young black man running through their Georgia neighborhood, and shot him dead in the street. And the prosecutor who originally passed on the opportunity relied on a rarely used legal statute to justify his decision: a citizen’s arrest.

George Barnhill, the district attorney in Waycross, Georgia, declined to prosecute Gregory McMichael and his adult son, Travis McMichael, after they jumped in their truck and confronted Arbery near Brunswick, Georgia, on Feb. 23. They told police they thought the 25-year-old black man was a burglary suspect and that when they confronted him, Arbery attacked them.

The Arbery family, however, insists the killing was racially motivated and has repeatedly demanded criminal charges.

The case is now in the hands of its third prosecutor after the two previous ones recused themselves because of their personal or professional ties to the McMichaels. That DA recommended this week that a grand jury review the evidence in the case — including a video of the moment Arbery died — and decide whether to bring charges against the McMichaels.

Citizen’s arrest has been part of the Georgia penal code for decades — although most people know it as a comic feature of the Andy Griffith Show. The idea dates back to English common law, when private citizens would be authorized to detain a criminal suspect in the absence of law enforcement. According to Ira Robbins, a professor of law at American University who’s studied the doctrine, almost every state now has some form of the concept, either in case law or in its criminal code.

“It’s going to come down to the facts. What did they actually see him doing?”

But the circumstances of its use can vary — and can be quite specific. In most cases, people who think they’re executing a proper citizen’s arrest are actually breaking the law. And linking the law with self-defense could be a slippery slope.

“The public doesn’t know — and likely cannot understand — the nuances of citizen’s arrest,” Robbins told VICE News. “That’s why it is so dangerous for people to take the law into their own hands.”

In 2014, for example, a man attacked a George Mason University professor during a lecture with pepper spray and attempted to place him in handcuffs, in what he claimed was a citizen’s arrest. The attacker was later charged with abduction and malicious injury with a caustic substance.

Georgia’s citizen’s arrest statute requires that the person doing the arrest has “reasonable and probable grounds of suspicion” that the person they were attempting to stop had committed a felony. It also requires that the citizen making the arrest “use no more force than is reasonable,” according to Matt Kilgo, a Georgia defense attorney who specializes in firearms law.

“It’s going to come down to the facts. What did they actually see him doing?” he said.

Kilgo has hardly ever seen a citizen’s arrest come up. It’s primarily used in cases of locals who intervene in misdemeanors, like teens speeding in a residential area or store owners who detain shoppers suspected of shoplifting.

“But as a justification for a death? No,” he said.

“Rosetta Stone of vigilante violence”

Barnhill, the earlier prosecutor on the case, raised the prospect of citizen’s defense in an unusual letter he wrote while in the process of recusing himself from the case, to the investigating police captain. It was later obtained by the New York Times.

Barnhill laid out, in precise detail, that the McMichaels were legally carrying their firearms under Georgia law, and that he believed their actions were appropriate under the state’s statutes for self-defense and a citizen’s arrest.

“It is our conclusion there is insufficient probable cause to issue arrest warrants at this time,” he wrote.

The inclusion of citizen’s arrest solved a thorny legal problem: Self-defense, including under Georgia’s broad Stand Your Ground law, is typically not valid when the shooter initiates the encounter. The laws do allow people to defend themselves without any “duty to retreat.”

But combining Stand Your Ground laws, which were popularized after George Zimmerman’s shooting of Trayvon Martin, with a citizen’s arrest could theoretically undo that — allowing someone to both start a conflict and end it violently, all while claiming self-defense.

That would create a scenario where “the ‘good guy’ can go anywhere they want, and then instigate a confrontation in the interest of arresting a quote-unquote ‘bad guy,’” according to Caroline Light, an expert on the laws at Harvard.

“Barnhill’s letter is like the Rosetta Stone of vigilante violence,” she said.

Kilgo, the firearms lawyer, has seen the combination of legal rationales used only one other time: a still-pending case in Clayton County, Georgia, when a white woman shot a black man after chasing him down following a hit-and-run. She was charged with felony murder. The woman’s attorney did not respond to a request for comment.

In the Arbery case, it’s still unclear if the facts support Barnhill’s analysis of the case. On a recording of a 911 call made on the day of the shooting, Gregory McMichael told the operator, “There’s a black man running down the street,” and that he believed him to be the same person who’d been caught on tape burglarizing neighborhood homes.

According to the police report, the father and son then grabbed their guns and hopped in their truck. As they drove, they asked Arbery to stop and ended up getting out of the vehicle. They told police Arbery began to attack Travis McMichael, and the two started fighting over his shotgun. That’s when he fired two rounds at Arbery.

Three prosecutors and more than two months later, a grand jury will now have to decide if that meets the standard for reasonable suspicion.

For the Arbery family attorneys, the answer is obvious.

“Mr. Arbery had not committed any crime, and there was no reason for these men to believe they had the right to stop him with weapons or to use deadly force in furtherance of their unlawful attempted stop,” attorney S. Lee Merritt said in a statement earlier this week. “These men were vigilantes; they were a posse and they performed a modern lynching in the middle of the day.”

Cover: In this Tuesday, May 5, 2020, photo, Keith Smith speaks to a crowd as they march through a neighborhood in Brunswick, Ga. They were demanding answers regarding the death of Ahmaud Arbery. (Bobby Haven/The Brunswick News via AP)