I think the police were at a disadvantage at the start of the investigation. Because this sort of thing doesn't happen in a place like Evansdale, I think that investigators initially gave the benefit of the doubt in assessing the situation and assumed that the girls had wandered off after parking their bikes at the SE tip of the lake. Crime scene tape was added on Saturday morning. It's possible that the bikes and area immediately surrounding the bikes were not preserved. More than 1000 people searched the areas around the lake and, when the girls were not found, investigators looked in the lake. Police stopped vehicles in the area, which I think was a really good thing. It's quite likely that the person that did this was in the area to see what police were doing. I'm sure that they already have the name of the guilty party, but I doubt they know who it is.
I doubt that police have any idea what happened. I think that the investigation was complicated, slowed down, because police decided to explore the drug angle. I suppose that's all they had to work with, but I think it's rather farfetched to believe that an angry druggie would stalk a 10 year old child (that lived with her grandmother) to another city, where she was visiting her cousins, and then abduct both the 10 year old and her 8 year old cousin. That, to me, seems like complete fantasy. Why wouldn't an angry druggie abduct the 16 year old child that lived with the father if the angry druggie wanted to lash out at the father?
Now that the bodies have been found, police can probably narrow down their focus. Assuming it is true that the children were murdered shortly after they were abducted, then I think that the focus should turn to a sexual predator. I think that everyone in the areas between Evansdale and 7 Bridges Park should review what they were doing on the weekend of July 13, and anyone that was out of town should have a good look at any family members that remained at home. Someone had business in Evansdale that morning and that person was not accountable to anyone for a few hours in the afternoon.