We don't know if she told the police this already, however, and she very well could have. The problem with interviews is they're edited and we don't know if she hadn't told this prior.
This does support Lee's earlier comments that Casey was more likely to tell him things than his parents.
I don't believe Casey... I think she was negligent in her daughter's death and perhaps caused it directly. If that's true (and I'd LOVE to be wrong and have Caylee be alive and well) then I hope she's punished as harshly as the courts allow.
As for the rest of the family, they may very well be victims as well.. and until the facts unfold I personally need to give them the benefit of the doubt.