Yes. I imagine that if the hair is still there, they can have a clue on whose DNA to test against first, or if the stature is smaller. I'm not sure how tall Justin is, but that could be why they were able to immediately discount him as a possibility. That seems quite far from Shannon's home.... how far would that be to drive? Walk? That would suggest that if her, she could have been 'dumped' there, as opposed to met up with foul play there. I wonder if hubby's car was ever forensically examined?
My thought is that if Justin can be ruled out, then this could very well be a female body. That opens the possibility of Shannon, or perhaps someone that has not been reported missing ... a new immigrant, or a visitor.