There is a reason police focused primarily upstream on there search of the area. They did use dogs. I don't want to comment on what police have not released at this time.And why do you feel that she was placed on the east side of the culvert and found on the west side, if that isn't too intrusive for you to answer.
Personally I think it has a great vantage point of traffic from all 3 directions and is a convenient location to back in and place a body into the culvert.