This is one of those things where LE is dammed, regardless of what they do. If they get the tape and investigate the sighting, it's reasonable doubt for casey, because they are still looking for a live child. If they don't get the tapes, it's reasonable doubt, because there will be a juror that will think, "well, they don't have a body, and they won't look for the child, they want to hang this poor woman."
ARGH!!!!!!!!!!!
This is why LE should never back themselves into a corner like this. Now casey will never be forgotten, because this case will end up in the textbooks.