This is just my opinion, and I really hope I'm wrong on this, but I really think her fiance, John Carter and one of her friends were involved in this.
I know everyone handles grief in their own way, however at the volunteer searches and gatherings, he just does not seem concerned, the same can be said about one of Katelyn's friends. With John Carter, he just seems to lack all emotion, and not as a person who is in shock, those people almost seem zombie like, no this guy is just going on with life as if Katelyn is not missing at all.
As for the friend, I won't name names, but several people on FB who have been trying to spread the word about Katelyn's disapearence and keeping us updated about the searches and such, have had really nasty messages sent to them by this person, which I just find odd, since they are only trying to help.
Again I really hope I'm wrong, these are just my observations.