I can see how the guy with the gun gets charged with murder but I can't see how the other two got a murder charge. They were there and they were following Arbery but they didn't pull the trigger.
Honestly I haven't followed that trial closely so I don't know if there are other factors at play. Like if for example they yelled "shoot him" then now they are contributing.
Also, Arbery was supposed to be in the neighbors house for quite a while IIRC so I think they have a decent case to argue they had reason to be suspicious. I don't know how well they made that case though.
With all the terrible news reporting on the Rittenhouse case I need to find a good reliable news source to help me understand the Arbery case better.
The three men acted in concert to chase, trap, and detain the deceased. They all Intentionally aided or abetted the in the commission of the crimes right up until the shooting.
According to Georgia law O.C.G.A. §16-2-20, every person concerned in the commission of a crime is a party thereto and may be charged with and convicted of commission of the crime.
Georgia is actually more lenient than many states. Georgia allows for defenses based on no criminal intent, that the associate was "just at the scene" but took no part in any facet of the crime, or didn't encourage the illegal acts.
Some other states can charge you with the highest charge even if you decided to stay home but had a hand in planning or providing material support (with knowledge) to the crime. I just heard of a guy who helped plan a robbery, decided the day of to stay in bed and not participate, and was later arrested when his co-conspirators told Cops he was in on the planning. Imagine getting rousted out of bed by SWAT for your buddies' crimes committed while you slept! In those cases, if you did nothing to prevent the crime or alert authorities prior to it, you can't claim you were not part of the conspiracy.