I agree
@iluvmua, if he was a police officer or former police officer (his employment dates with the PD haven't been verified yet that I know of) he may have had access to a blue light. The family has always said the girls wouldn't have stopped for anyone other than an officer.
Someone mentioned earlier if he possibly followed them from one of their stops while trying to find the field party but that just seems to be too much work and I think they would have noticed someone following them especially at night on rural roads. Of course I could be totally wrong too.