Whenever we get a story in the news about a police shooting an unarmed black man, or of a black person who is murdered by a white person who is then not arrested, the right-wingers always come out of the woodwork to defend the perpetrators. They do this by victim blaming - coming up with every ridiculous reason to try and make the victim look like the aggressor.
So for the Ahmaud Arbery case, this is what happened: Ahmaud Arbery is spotted on some surveillance video looking around a construction site. He does not steal anything. This ex-cop who apparently had prior history with Arbery gets four other guys, and they go out and ambush him. The ex-cop and his son are armed with shotguns. They find him jogging down the street, surround him with their pickup trucks, and point their shotguns at him. A fight ensues, and Arbery ends up dead.
According to Georgia law one can do a citizens arrest if they either witness a crime, or have immediate knowledge that a crime has been committed. So you may say, well trespassing is a crime, correct? However that's not good enough, the crime has to be a felony. Since nothing was stolen, and the security video didn't show Arbery taking anything, then no felony was committed. Thus these four assholes had no legal right to peruse Arbery and attempt to arrest him. Please keep in mind these people were not cops, so Arbery is under no legal obligation to obey their instructions.
Those are the facts of the case. Since this is a black person who was shot and killed by white people, then all the racists and white nationalists and 2nd amendment people and other assorted right wingers are coming out of the woodwork to blame the victim. This shit will keep happening, what you can do is keep the facts straight and argue for the truth. Don't fall for it, and push back. This guy wasn't the aggressor. He was murdered. He was the victim.