I like your thought process.I have not, until the recent discussion here, really thought about an accomplice, but when you read about some crimes, there is some one who is a prime actor and then that person entangles others, and they always seem to be "followers" who get in the middle of things that spiral out of control, IMO. (still not convinced that there was an accomplice, but if LE was really talking to two different people, and if BG did "move around really fast" maybe at some point he got a ride from one point to another. He could have just told some one that he tripped, got really wet and muddy and needed a ride home, I guess.) All speculation.
When I look at a crime I ask myself what is the smallest number of perpetrators who could handle this crime - speculation. But it’s much better to have evidence. Since we haven’t been given evidence that there was more than one perp, I stay with one.