My theory can apply to either one, or any pair of guilty party and unwitting accessory. It makes sense for the one who committed the crime to saddle the innocent one with the evidence to set it up to appear that the accessory is a co-conspirator. Especially if one felt that the accessory was uncooperative or apt to turn in the murderer. By telling the accessory that all the evidence is planted on their property alone, the murderer stacks the cards up against the accessory in such a way as to make them far less likely to rat the murderer out for fear of spending their life in jail as well. It makes perfect sense to me, actually.
I never mentioned anyone's socio-economic status, but now that you bring it up, I still think it is far more likely that a man without a vehicle would steal one before a man who already has several. I also find it more likely that someone who has a record for multiple arrests would be more likely to instigate a crime than someone with a clean record.
I also don't think that there would be a DI on a cooperative witness, but I do still believe that if LE were concerned about the safety of one of two co-conspirators, they would put that one into protective custody. Personally, I don't think that the crime itself is enough to provoke random inmates from preforming jailhouse justice on the accused, otherwise they would both be in protective custody. But if authorities feared an attack from one of the two against the other, in my opinion, it would more likely be the instigator of the crime who would be the attacker, to make sure to keep his witness or accessory quiet. I don't know if I have ever heard of a murderer who needs to be protected from the reaches of his unwitting accomplice while in jail.
