It's not that they have to know how the person died, but they have to know it was a murder. The SA only gave two theories on it being a murder, the duct tape and chloroform. The DT gave the theory of an accident. This means the jury had three choices: she died by the duct tape, she died by the chloroform (or both) or she died by accident. If they didn't believe she died by the duct tape or chloroform there is absolutely nothing showing that Casey KILLED Caylee. The 31 days, the partying, the body in the trunk, the lying all of that doesnt prove that she killed her, it just proves that she was a horrible mother, she lied and that she covered it up. Im NOT saying I believe this, because I do believe that she was responsible but without the Duct Tape/Chloroform there is no proof that Caylee died by the hands of her mother.