I don't know if Casey did it or not, but I think we need to see more solid evidence for a conviction for murder 1.
To me, the duct tape screams sex offender. Recently in May I believe, a sex offender was charged with a similar offence in the same area - he lived just a few streets away. He had entered a house, taken the toddler (a girl) & bedding from her bed, dressed her in a pair of shorts, placed her in the garage and placed a pair of high heeled shoes next to her. The child woke up and pulled the duct tape off, waking up the parents who chased the offender but didn't catch him. He was later arrested on DNA evidence.
My horrifying thought is this. If he had done this to Caylee but she wasn't lucky enough to pull the duct tape off, he could have disposed of her in the trunk if the car was open in the garage, and this is a possibility given that they drive the car in there to take washing etc. out of the trunk. George had been at work the night of 15th so its quite likely Casey would have driven in because there would have been a space.
It would also explain why Caylee was wearing shorts, why the items with the body come from the house, why the duct tape, laundry bags and garbage bags are consistent with those stored in the Anthony garage, and why Caylee's shoes are missing. Casey might be driving around with a mystery smell in her car until she opens the trunk......
It would also explain why the cover-up. Firstly it would be incriminating for her. Secondly if she had later told her father, he may well have thought she did it. She may even have thought that he did it. But he would have helped her cover up because it would "kill Cindy". Casey herself may have thought that someone who was trying to teach her a lesson had done this given that she admitted herself that she had stolen money etc. It would explain why she didn't go back to the house while her parents were there, because it would be an intolerable situation, better to go elsewhere, get stoned, dissociate. It would also explain many of the family's inconsistencies in that Cindy doesn't know what happened but George and possibly Lee know more. Perhaps she went to Tony's on the 16th thinking her mother had taken Caylee, and didn't discover the horror in the boot until the next day. It may explain why she borrowed Tony's car to go to Chris's on 17th - couldn't risk him wanting to look at her car..
It sounds outlandish I know, but it's not so uncommon these days. In the next street to me, an offender was recently caught with a knife and a stocking over his head, interfering with a 6 year old boy who woke the parents & the father caught him.
It wouldn't explain why the family are still claiming that they don't believe the remains are Caylee.