Why didn't Baez just say Casey covered up the drowning?

You're right. It would at least be believable. The drowning scenario just doesn't make sense and no jury is going to believe that...given the fact the duct tape on Caylee's face, the chloroform etc. So that would make it a case of manslaughter or negligent homicide or something like that. Plus maybe *abuse of a corpse* and lying, perjury, making false reports, etc. Lots of charges that would put her away for many many years.