These folks are not that sophisticated to have a secret plan. Heck, MS didn't even make sure his phone was fully charged.
MOO
Which, to me, imo, leads me to wonder if he knew ahead of time, that this would be an all-nighter, as one would expect it to be if murder was in the plans. He (MS) and MM were constantly communicating.. and MM also was aware that the two would be stealing a truck. It is no wonder that she was completely freaked out by the next morning and wondering if he was dead, having not been able to reach him. Interesting that she wondered if he was *dead*, as opposed to that they had been caught and arrested? moo