Statistically speaking the boyfriend is likely.
In this case, he may very well have had nothing to do with it and has his whereabouts elsewhere at the time accounted for.
Good for him.
This case is a strange one for sure. I have been in that area (Grinnell) and it is essentially the middle of nowhere. You can be on a deserted road in minutes.
Keep in mind that someone else from the University of Iowa considered her his girlfriend, or even a stalker from her California high school.