Bill Cosby claims immunity from sex attack charge over case '˜promise'

A key piece of evidence in the sex assault case against Bill Cosby has been called into question, according to reports.

Comedian Bill Cosby is at the centre of sex attack claims. Picture: AP

An email seen by CNN ­alleges that a prosecutor promised Mr Cosby’s deposition in a 2005 civil case would not be used to bring criminal charges.

In the deposition, Mr Cosby admitted drugging women during sexual encounters but said it was by mutual consent.

The statement forms the basis of an aggravated indecent assault charge. which Mr Cosby denies. His lawyers will now use the immunity claim to get the case dismissed.

Former Montgomery County, Pennsylvania, district attorney Bill ­Castor was in charge when Andrea Constand sued Mr Cosby in a civil sex assault trial in 2005, after no criminal charges were brought. Mr Cosby settled the case for an undisclosed sum.

Mr Castor, says CNN, agreed Mr Cosby’s deposition would not be used to bring criminal charges.

However, current ­district attorney Kevin Steele said there is no evidence of a signed immunity agreement, which would have had to go through agreed channels.