What this will come down to in court, is whether the defendants could have avoided killing the victim. The answer is, "Yes". The next question will be, "Then why didn't you?"
The defendants admitted that they "Chased him down." Had they stopped chasing the victim down, the murder could have been avoided. Had they stayed in the truck, the murder could have been avoided. By calling 911 before they started chasing the victim, the murder could have been avoided.
The fact that they had options to prevent the murder and murdered the victim anyway, is why the shooters are facing murder charges.
They chased down and murdered an unarmed man. Guilty.