Long time lurker on this case (giant THANK YOU to all posters--my brain feels like it's been doing some advanced form of yoga...). Will try to keep this post focused & not repeat too much as I think this out loud:
1. In terms of direct tangible evidence, there is no direct link between Gatorade bottle/syringe/contents and Casey, no fingerprints etc. At least not that we know of yet.
2. Bottle/syringe contents are among several coincidental appearances of "chloroform" in this case.
3. Written notes on doc dumps indicate some LE interest in chloroform levels related to this case.
3. Casey had several different means of acquiring a syringe which could include either or both testosterone and chloroform, such as the syringe which was found 1 foot from her dead child's skull.
4. The remains were scattered. I seem to recall that the head and torso were in one location with various extremities moved away from that site. (God I hate to even type that.) IF these items turn out to be in fact related then it either both were dumped at the same time, or that the killer returned to same scene to dump bottle containing potentially-incriminating-to-hoped-for-scapegoat-JR syringe later... OR that the items are unrelated and the bottle either pre-dated the placement of the body, or post-dated it and whoever dumped the bottle failed to report anything suspicious...
Posters have questioned whether Casey was the sort of person to return a needle to its cap, then bag it, then put it in a bottle, THEN dump same in the same area as Caylee's body. I think yes, if only because she would not have wanted to stick herself with said needle.
I have heard from more than one friend in LE that when it comes to solving crimes, the simplest answer is usually THE answer. I wish there were more simple answers here. And I appreciate all your work in sorting through this tangled ball of possibilities!