Sorry, one more observation--
I just noticed that there is a cell phone tower, that would have been probably the only tower providing the service to the girls' cell phones throughout the whole incident. It is located near the intersection of Route 75 and E1140 (on mapquest), southwest of the crime. Generally, there is recorded data for the "pings" that occur regularly between a tower and phone. This data includes the phone number, time, and strength of the ping. Judging by the strength of the ping, one can estimate the distance of the phone from the tower, but this can be distorted by a lot of other variables. But that strength may be able to tell LE something.
For example, a sudden increase in strength that remains could have indicated that the girls left their house. As they walked north to the bridge, the ping strength would decrease (and a tower north on Route 40 might have been able to pick up their ping). As they returned south, the ping strength would increase. Based on this data, LE should be able to construct quite the timeline of events. In addition, they would have the numbers of anyone having cell phones in the area at that time. In this way, they could corroborate witness stores, and identify others who may have been in the area who have not come forward. And they should be able to identify who was traveling through that area, as opposed to staying in a single place during that time. And this isn't a very populated area, so there the number of phones/people to check are limited.
When I realized this, it just made me more confident that OSBI has a pretty idea where they are going with this case.