My two cents....In a case so high profile, when we know the FBI was already involved to some extent, I have to believe they have brought in an FBI profiler to look at this case. I imagine the expert testimony of this person may end up being your smoking gun. Here's why (according to books I have read on the subject):
1) A profiler will talk about the reasons children are kidnapped, since KC herself claimed Caylee was kidnapped. The reasons are:
a) sicko perverts who prey on children - overwhelming odds would make this person a white male with priors, not your trusted female babysitter with a family of her own.
b) someone who desperately wants a child, but can't have one for whatever reason - again, ZFG would not fit into this category
c) for ransom. Which would be, logically from someone who has money and/or a job, which KC had neither. Also, a person asking for ransom would make a ransom demand. Didn't happen in this case.
#2 The Heart Sticker
Profilers talk about several different aspects of a crime. In a murder, there are things that are present out of necessity - a gun or a knife, duct tape perhaps. They serve as tools for the criminal to commit the crime. Yet often, there are other things present that are not necessary - at least not on the surface. They are not necessary to commit the crime, but they are very necessary in that they fill a need for the killer. Think of a crime scene where the word "B#tch" is written in lipstick on a mirror, to use a cliche example. This action only serves to satisfy the killer, in this case, express his rage. This is where I think a profiler will go with the heart sticker. It's not necessary. Only to the killer would it have meaning and purpose. Yet, it doesn't speak of a killer who wanted to degrade his victim. To me, it more reminds me of a mother putting a "band-aid on a boo-boo." Momentary remorse, perhaps, but not true remorse, else the child would not have been discarded so carelessly.