Perhaps because the tiny body was wrapped in blankets and/or towels and then layered in plastic bags. Then, put into a plastic box of some type and that wrapped in plastic bags and sealed, then finally, that package wrapped in plastic, sealed, and put in another plastic box. Then that box to be sealed with the tape from the dispenser that was taken from the house. Sort of like a "nesting dolls" situation. This "package" could have been transported for the short distance to the river and not be detected by the dogs. This is a simple scenario, and what I believe happened. I don't necessarily know that Lisa was taken in the family car, but I'm sure in my heart about the rest...