I'm thinking the car may have been the key to locating Waters, too. Considering how vast and remote the areas of Montana and ND as people have described here, if the suspects drove onto back roads looking for an isolated spot to dispose of a body, what if they got lost and couldn't find their way to the main road? Maybe the tipster is someone the suspects asked directions of and he was able to give a description of the vehicle to LE when he became aware of Sherry's disappearance and remembered the curious encounter. But, LE would have no idea how long or in which direction the two had been traveling before stopping to ask directions. It would be kind of amusing to find out that getting lost led to their capture.