I think we'll find that Casey used her "research" into "household products that kill", and filled a syringe with her poison of choice, and injected Caylee with it. In my opinion that is why the weed killer and other chemicals were seized by LE during the subsequent search and seizure of items right after the remains were discovered.
Sadly, since there was no viable tissue left on Caylee's remains, there is no way to verify the presence of an injection site. However, even though it's been stated no prints were pulled of the duct tape, that doesn't mean that prints weren't lifted off of the Gatorade bottle or syringe. If the sediment in the syringe turns out to be a household poison, with Casey's fingerprints all over it, at least there will be a more clear cause of death.
The fact that LE stated emphatically in their report that death was not accidental but intentional points strongly to the presence of clear evidence indicating an intentional act designed by Casey solely to cause the death of her child.