Jane and her boys were enroute between Grand Rapids and Escanaba, Michigan by car - a distance of about 400 miles (driving time about 6.5 Hours). Gaylord (where the rest stop was) was about half way to their destination. Nobody would have tailed them that long without being noticed. Also, nobody would have "targeted" Jane specifically, trailing her for over 3 hours.
The attack on her was, no doubt, a crime of opportunity, committed by someone who happened to be at that rest stop - either by happenstance, or by design awaiting a random victim. The chances of the killer being someone Jane knew are almost zero.
The police may have noted that there were no other cars around when they finally showed up at the rest stop, but keep in mind that some time had gone by between the boys and their mother first entering the restrooms, and the time the boys went in looking for her, finding her, and flagging down a car for help. There easily could have been someone else (with or without a vehicle) at that rest stop before they arrived, and there was plenty of time for him to leave after killing Jane.
Jane was viciously attacked and stabbed 23 times. This is not someone who accidently jabbed her while sharpening his knife, or who thought he was defending himself. It was not a "one time" thing. He was an evil, cold blooded killer who had done this before and after. Looking at other similar attacks might provide leads to who he was.
It is possible that he had previously been in prison for a violent offense, and may have been in contact with others of similar mindset. Did he talk to other inmates about his proclivities? Did others offer him advice? Someone this out of control would sooner or later end up in prison (or shot by someone in self defense). Questioning inmates who are known to have committed similar murders or attacks might be worth while.
