What physical proof is there is get a conviction in the Casey Anthony case of murder?

I have been watching it a lot more in the last week, and I see lots of proof for child neglect and of course proof that she is not a good person, but what physical proof do they have to get her convicted of physically killing her daughter, and enough evidence to get the death penalty. I see lots of lies and circumstantial evidence, but no "smoking gun" for lack of a better word?