I’m not sure where the story developed that the McMichaels were intending to “arrest” Arbery. Based on other reports, it’s likely they were going to talk to him about the recent break-ins, but thought that he might be armed and brought guns for their defense. If they had intended to shoot him, why would they have ever allowed him to get within an arms reach of the shotgun? It seems to me that Arbery was the one who escalated the situation and the McMichaels were caught by surprise at the agression.
I’m not sure where the story developed that the McMichaels were intending to “arrest” Arbery. Based on other reports, it’s likely they were going to talk to him about the recent break-ins, but thought that he might be armed and brought guns for their defense.
The elder McMichael was a Glynn County cop for seven years and then an investigator for the DA's office for thirty years. I believe it likely that he knew the statutes on citizen's arrest. That is what arguably authorized the pursuit and attempted detention/arrest or questioning with a shotgun in hand. It is what would have arguably made the brandishing of weapons legal.
The elder McMichael, fairly recently retired from the DA's office, very possibly knew of Arbery's prior record, including for felony unlawful concealed carry of a firearm at a local high school basketball game.
An arrest may be defined as a substantial physical interference with the liberty of a person, resulting in his apprehension and detention. It is generally effected for the purpose of preventing a person from committing a criminal offense, or calling upon a person to answer or account for an alleged completed crime.An arrest may be effected “actually” or “constructively.” An actual arrest occurs when a duly empowered law enforcement officer intentionally employs physical force (e.g., a physical touching of the person), and delivers a formal communication of a present intention to arrest (e.g., “You are under arrest!”). A constructive arrest occurs without an intentional use of physical force and without a formal statement indicating an intention to take the person into custody. Moreover, in constructive arrest situations, the power or authority of the arresting officer, along with his or her intention to effect the arrest, is implied by all the circumstances surrounding the encounter. In either case, to determine whether an arrest has occurred, a court will examine whether physical force has been applied—which may be accomplished by a mere touching of the suspect—or, where that is absent, whether there has been a “submission to the assertion of authority.”
Larry E. Holtz, Criminal Procedure for Law Enforcement and Criminal Justice Professionals, Matthew Bender & Company, Inc, 2015, p. 1
You do not really have to hear you are under arrest. Two guys with guns saying they want to talk to you may be a sufficient show of authority to get the job done. Had Arbery submitted to their show of authority, and not felt free to leave, that could be constructive arrest. This is probably known to a 37 year member of law enforcement and seemed apparent to the District Attorney.
DA George Barnhill wrote:
Third
It appears Travis McMichael, Greg McMichael, and Bryan William were following, in 'hot-pursuit', a burglary suspect, with solid firsthand probable cause, in their neighborhood, and asking/telling him to stop. It appears their intent was to stop and hold this criminal suspect until law enforcement arrived. Under Georgia Law this is perfectly legal,OCGA 17-4-60 A private person may arrest an offender if the offense is committed in his presence or within his immediate knowledge. If the offense is a felony and the offender is escaping or attempting to escape, a private person may arrest him upon reasonable and probable grounds of suspicion.”
I would not necessarily recommend anyone emulate the McMichaels. A court could find they did not have reasonable and probable suspicion, and then they are in very deep kimchi.