Police need to look closely at the brother, it just seems strange that he was there at the scene, of what we all believe is a crime, but really doesn't have a good reason to be there, or behave in a normal manner. It is possible the brother was having an affair with Brandon's wife, the decision was made to get rid of Brandon, to which the brother was supervising, i.e., a part of. Some guys confronted Brandon, and he got in his truck and took off. His truck runs out of gas, but he gets out of the truck and runs off into the darkness, probably injured from the original confrontation. Perhaps it is at this time the brother, who was also in pursuit, (knowingly or unknowingly to Brandon) arrives at the scene, where he fends off the responding officer and explains Brandon has left the truck.
If this is a crime, then the brother was at the scene of the crime, (with an empty gas can) and that cries out for an explanation. No person would tell the deputy, that their brother, "stepped away" when he is in the middle of nowhere very late at night.
Something is off between Brandon's wife, who wasn't answering the phone, and Brandon's brother, whose actions seem all but concerned. Clearly Brandon was being pursued, it can't be a coincidence the brother was in the area in and around this same time, and rather than ask police for help, sent them away as though there was nothing really to worry about.