Now, the article explains why this couple would be suspects, and even has some evidence (such as buying tacks). However, it does seem a little strange to me to hear that their guilt is just assumed. I realize this isn't a major criminal investigation, but really, anyone could have done it.
Yes, they have a bad history, including calling the cops to the point that they no longer respond. I'll even go so far as to say they are likely involved. But we can't just assume their guilt, or what we are doing is far worse than scattering tacks on a trail.