When Arbery was in school, he was in a group of guys who brought a gun to a basketball game. They all got charged with felony gun possession because it was a school. Arbery apparently got busted shoplifting in 2018, and the Dad was involved in the investigation that led to revoking Arbery's probation.
The son of the Wayne County DA (the second DA in the case) works for the Glynn DA, and led the case. So Arbery was known to the Dad - and by extension probably the son, and the conflict of interest with the second DA was known at the time the case was transferred to him.
My theory is this - In January, young McMichael's pistol was stolen out of his unlocked pickup at his Dad's house (that is the only theft reported in the neighborhood from December thru the day of the murder). Daddy had seen Arbery jogging thru the neighborhood and began to suspect him. He made sure to pay attention the next time he saw Arbery, and then recognized him from the case in 2018. Daddy probably called in a favor and got access to his file to confirm who he was, then they planned to confront Arbery next time they saw him. The point of the video was them thinking that the black guy would attack when confronted, and they wanted evidence that they were defending themselves. The also wanted to have "trophy" photos to share with friends. It blew up in their faces, and Daddy called in favors immediately, and the cover up began.
Favors are common occurrence between GCPD, the DA, and County Commissioners. It's how this almost got covered up. Its how the DA tainted a case to protect 2 GCPD officers who killed Caroline Small, and its how one of those cops was then later allowed to avoid charges of domestic violence and stalking just before he killed his ex-wife. It's also how the "suicide" of County Commissioner was covered up. Amazing how a guy with his hands zip-tied behind his back can shoot himself in the temple and then jump into the river after a night of gambling with another commissioner and the police chief.
****. I make it sound like this place is terrible and there are a lot of days I wonder how the GBI or FBI has come in and shut everything down. It really is a great place to live and raise a family, but damn the system is corrupt.