The Crime of Casey Anthony

Single mom gives birth to a daughter, has her own problems and cannot cope with her baby. For some reason - post natal depression, desperation, wickedness; we know not what - she kills her. Simple. Black and white. Except, of course, that is not how it was. As of today, nobody has been convicted of Caylee's murder. It is not even clear that she was a victim of homicide. Casey has served time, but for relatively minor crimes associated with her daughter's disappearance.
She is not a convicted killer. Therefore, she is not a killer. Not in the eyes of the law, and therefore, not in the eyes of society. At least, that is how it should be. But not, maybe, how it is. A troubled girl, yes. A confused girl. Definitely. Even possibly a victim herself. An alleged target of domestic sexual abuse. But the question remains. Why wasn't Casey convicted?