Do you mean use dogs to track down the perp? This would have been impossible here because the dog needs to be first given an item with the scent that it is supposed to track, i.e. a recently worn piece of clothing. Since the perp (presumably) didn't leave any belongings behind LE would not have had anything to offer the dog as a reference sample. On the other hand, tracking dogs could have been used (and maybe were?) to find Abby and Libby if their family had provided LE with recently worn clothing or bedding of theirs. However, even then there are lots of factors that would make it difficult for a dog to track. Being high up on that bridge and possibly on a windy day their scent would become untraceable. Cadaver dogs could have also been used to find their bodies if they had been missing longer. But again, tracking the perp would be impossible because there is no scent sample available. These dogs are smart, but they do need to be given a point (or scent) of reference.
http://www.newsandtribune.com/india...cle_dfef61b5-ad9e-5a87-8329-1f66aaa8719a.html
It says volunteers were told to stay away and not contaminate anything because the search dogs were out at one point