You're wrong about that. You don't need "bloody hands." MOST criminal cases are circumstantial--and there was a busload of circumstantial evidence in this case. The problem is that jurors don't want to use common sense and draw a conclusion--hell, our whole educational system today teaches people that common sense and conclusions are bad.
I never heard anyone say they saw Casey with the dead body or heard her confess or her fingerprints on the shovel or even sufficient motive to kill. For all we know, the grandmother or the brother could have done it.
You really need a lot of blood for a case like this. Then there is the “accidental drowning” theory that hung in the jury’s mind. The prosecution seemed to be unknowingly pushing that for a while.