Suppose you are driving down to WDW alone with your DD. You stop at a gas station to let your DD use the restroom. She goes in alone but never comes out. You go in to find she has been murdered. You were the last one to see her alive so you must have been the one to murder her; right?
There are issues with your analogy.
First off, I think most reasonable people would enter the bathroom, see their child, check for signs of life, and call 911. They would also be incredibly distraught by the event...and I doubt they'd be seen at a video store, or out partying with friends, in any proximal time frame.
I doubt most (or even many) parents would find their child, worry instantly that someone might think them responsible, back their car up to the bathroom, load their child in, wrap them in blankets and material already (not to mention readily and ONLY) found in their vehicle, drive a few miles away, dump the childs body, and then tell everyone the child was safe and sound, with someone else (or with you) and unavailable to talk. I also doubt that most (or even many) would concoct the charade and perpetuate it for 30 days.
Yes, it's true: That ALONE does not make the parent guilty of the death of their child. But the behavior is so out of character, and out of the norm, that it makes it hard to create any equivalent analogy to place someone else in Casey's shoes.
In addition, there are things in your scenario, above, that would generate pieces of evidence. The date/time stamp on the pump showing when you were pumping gas (assuming they're the standard digital pumps that all generate transactions...rather than the old manual pumps). Witnesses in and around the gas station. Possible (probable) security cam footage of the parking lot and/or interior of the store. Potentially your credit card transaction from pumping gas (or, the clerk's testimony who activated the pump when you went in to pay first). The physical evidence in and around the crime scene, itself. That's just to name a few of the dozens of potential pieces of evidence to support your claims that your daughter went into the bathroom, never exited, and you found her.
Again, I don't mean any of the above to comment on the verdict...just on the premise that something like this could happen to "anyone". It would take a "perfect storm"...which is potentially possible... for it to happen. But the above analogy isn't entirely apt, all things considered.