(NEWSER) – A Pennsylvania prosecutor's sexual assault case against Bill Cosby could be in deep trouble, according to an email obtained by CNN.

In the email, former Montgomery County DA Bruce Castor tells a successor that he made an agreement with Cosby that a deposition from a 2005 civil case brought by accuser Andrea Constand would not be used in any criminal case. "Unless you can make out a case without that deposition and without anything the deposition led you to, I think Cosby would have an action against the County and maybe even against you personally," warns Castor, who says he "can see no possibility that Cosby's deposition could be used in a state criminal case."

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