My apologies ahead of time, but there's no other way to explain it than to be graphic:
The chloroform/duct tape "accidental" theory (something bad happened): KC needs sitter. Chloroforms Caylee. Places duct tape on mouth to keep her quiet in case she wakes up, and leaves her in the trunk of her car. Caylee semi-wakes-up and she is nauseous, vomits and aspirates. Jimmy Hendrix died that way. So did Janis Joplin.... even though they DIDN'T have their mouths covered with duct tape. Yes, they weren't "chloroformed", but they overdosed and overdoses make you vomit. Maybe Casey used a bit too much chloroform - this time.
I have thought of this exact scenario. Duct tape was used to keep Caylee quiet, not intended to kill, but kill it did. KC had no sitter though she had asked CA. KC had plans and no child was gonna get in the way of those. So she put Caylee under with chloroform (and I am convinced KC had already done this to Caylee a few times since March after searching how to make chloroform). But this time the weather had changed and it was much hotter in the trunk, and Caylee vomited. She might not have even needed to wake up to do that; could have vomited while still out from the cf.
KC found the child dead in the trunk and then had to make plans on what to do. She had to do this on the fly because she had not planned on Caylee dying. She drove home, thought she might bury Caylee but found she couldn't accomplish that physically, so she found a place to dump the body.
In the Florida heat in mid-June the body would have started to decompose quickly, though there may not have been an odor noticeable to humans right away. Fluids from the body likely seeped into the trunk's carpet and that stain is what caused odor of decomp to build...slowly over time. Others could ride in the car and not notice any odor, though anyone opening the trunk might have noticed an odor even if they might not recognize it for what it was. The odor did not permeate the passenger compartment until the car had sat with both the car and the trunk sitting unopened for awhile.
That's all JMO, but I have had smelly garbage in my kitchen that didn't actually smell the entire house up and in fact was just barely noticeable right next to the trash can, yet very very smelly as soon as the lid was opened.
The car sitting at Amscott and then in the tow yard in hot humid weather is what caused the odor to grow. It got worse with each passing day, and eventuallly became noticeable in the passenger compartment.
ETA: If the above is what happened, it's still murder. Aggravated child abuse resulting in death is murder. Placing the duct tape on a child's mouth is most definitely child abuse and it was intentional. All the covering up any lying proves KC knew right from wrong...that what she had done was wrong and had caused Caylee's death.
