A former district attorney in Montgomery County, Pennsylvania, says he agreed more than a decade ago that his office wouldn’t use a civil deposition given by Bill Cosby in any criminal matters. This could spell big trouble for the case against the comedian.

Although the agreement was a verbal one it could still stand up in court especially if the former prosecutor agrees to testify about his claim. In the email, the prosecutor 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.

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.

Cosby appeared in court in late December and didn’t enter a plea. But through his lawyers, Cosby has steadfastly denied wrongdoing in this case and dozens of allegations made by at least 50 other women.

Earlier this week, Cosby’s lawyers filed a motion asking for the charges against the comedian to be dismissed.

In a statement, Cosby’s attorneys asserted that the charges were “illegally, improperly and unethically brought by District Attorney Kevin Steele and his office.”

According to the statement, the charges “violate an express agreement made by the Montgomery County District Attorney in 2005, in which the Commonwealth agreed that Mr. Cosby would never be prosecuted with respect to the allegations of sexual assault made by complainant Andrea Constand.

“This agreement, made for the express purpose of inducing Mr. Cosby to testify fully in Ms. Constand’s civil litigation against him, led Mr. Cosby to give deposition testimony in 2005 and 2006 without invocation of his Constitutional rights against self-incrimination. Now, to fulfill campaign promises, the newly-elected District Attorney has repudiated the agreement and has based these criminal charges on the very testimony Mr. Cosby gave in reliance on the Commonwealth’s non-prosecution agreement,” the attorneys said.

Steele said Friday that his office would file a response to the motion to dismiss, which his office has said has no merit.

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