I'm fine with using circumstantial evidence to convict someone of murder one; i.e., provided it represents inculpatory evidence that has an extremely high degree of reliability.
However, you're largely assessing suspected behavior in times of stress. At best, behavior can be considered corroborating evidence, not inculpatory evidence. In other words, it's reliability is too low to be the central basis upon which someone can be convicted of first-degree murder.
Moreover. assessing behavior can cut easily both ways. It should be fairly obvious that if the state alleges Casey drove around with Caylee's body in the trunk of her car for around eleven days (it appears they will indeed claim this), that the defense will almost certainly maintain that Casey allegedly driving around with a body in the trunk of her car for that period of time works strongly against the state's notion that Caylee's death resulted from a planned and deliberated murder. And if Caylee's death was not planned and deliberated, murder one is off the table.
Not even, honey. The taped-up head argues for premeditation (I'm not really into the computer stuff-household weapons stuff, myself, BTW).
Not having made a plan for disposal doesn't obviate a lack of premeditation.
Moreover, in most cases wherein the killer has kept the body around, juries have not said, "Aw! That's not so bad. He was just under stress. He's prolly innocent. Maybe he just didn't notice that his wife's dead body was under the bed for a week."
Possession of the dead body IS a smoking gun, honey. Any juror will see it that way. That's substantiated by the dogs, the lab, and testimony re: the stench by the entire A family, including KC, herself.
Most jurors having children or having had children are NOT going to see that refusal to report or the partying hearty as anything but what it is: 1) guilty knowledge (refusal to report), and 2) a celebration of personal freedom, unencumbered by a child (partying non-stop).
Then, there is also no innocent explanation for KC and the As lies, obfuscations, and attempts at derailing the investigation. An innocent mother and family would do anything to help LE find a missing baby.
You can argue inculpatory and exculpatory until pigs fly. The jurors won't overlook the obvious. She killed her kid. And, her behavior is crucial evidence, as is the behavior of the perp in any other case.
Or, to put it in another context, the guy who has the money from the bank heist in his trunk is prolly the thief.