I wonder if they might find useful forensic evidence on the sticky side of the heart sticker, if it was stuck to the outside of the duct tape.
If the sticker was directly over her mouth but under the duct tape, there could be something left on the front of the sticker.
GA didn't mention Caylee talking to him the last day he saw her, as I recall. I've always suspected that Caylee might have been drugged the night before, resulting in unconciousness or coma. Casey could have fixed her hair, dressed her in clean clothes, put sunglasses and a backpack on her so that she could carry her past George as if she were just laying her head on Casey's shoulder. Casey could have used the knife to make sure she "never woke up" after she left the house.