A former district attorney in Montgomery County, Pennsylvania, claims he agreed more than a decade ago that his office wouldn't use a civil deposition given by Bill Cosby in any criminal matters, an email obtained by CNN shows -- a revelation that could call into question the viability of the criminal case against the comedian.
The 2015 email -- sent by former District Attorney Bruce Castor to successor Risa Vetri Ferman -- details an apparent verbal agreement the prosecutor had a decade earlier with Cosby's attorneys for Cosby to testify in a civil sexual assault case brought against him in 2005. In the email, Castor writes that his intent in making the deal was to create an atmosphere in which Cosby accuser Andrea Constand would have the best chance of prevailing in her civil suit against the 78-year-old comedian by removing the prospect of Cosby invoking his 5th Amendment right.
The email was sent three months before criminal charges were filed against Cosby in Montgomery County in December, and could call into question the viability of the case, CNN has learned.
In it, Castor writes to Ferman: "I can see no possibility that Cosby's deposition could be used in a state criminal case, because I would have to testify as to what happened, and the deposition would be subject to suppression.
"I cannot believe any state court judge would allow that deposition into evidence. .... Knowing this, 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."
The deposition is a key piece of evidence, cited by prosecutors as the impetus for reopening the case.
At the center of the case are allegations made by Constand, a former Temple University basketball employee, who says Cosby sexually assaulted her in his home in 2004.
Dolores Troiani, an attorney for Constand in 2005, told CNN's Jean Casarez on Friday that she never knew about any such agreement between Cosby's attorneys and prosecutors.
Castor, when asked by CNN about the email, declined to comment.
The current district attorney, Kevin Steele, who was elected in November after serving as Ferman's longtime top deputy, told CNN on Friday: "There is a specific legal method to grant immunity. That was not done in 2005."
Steele also noted that in Castor's 2005 press release declaring there was insufficient evidence to prosecute Cosby that Castor himself said he would "reconsider this decision should the need arise."