Bill Cosby's lawyers will ask a judge to throw out the only criminal case lodged against the TV star from the dozens of accusations that he molested women.
The defence will argue that Cosby had a deal with a suburban Philadelphia prosecutor in 2005 that he would not be prosecuted and should give evidence freely in accuser Andrea Constand's civil lawsuit.
That evidence, released only last year, prompted the successors of former Montgomery County District Attorney Bruce L Castor Jr to reopen the case and ultimately charge the 78-year-old comedian with felony sexual assault.
Cosby has not yet entered a plea.
Cosby admitted in the deposition that he had a series of affairs with young models and actresses; had obtained sedatives to give women before sex; and gave accuser Ms Constand three pills before a January 2004 encounter at his home.
He called it consensual but she said she was drugged and violated.
In an unusual twist, Mr Castor is scheduled to be the defence's key witness today.
He insists that he forged an oral "non-prosecution" agreement in 2005 with Walter M Phillips Jr, a Cosby lawyer who died last year.
It is not clear if anyone can corroborate Mr Castor's account.
However, Temple University board chairman Patrick O'Connor represented Cosby at the deposition. He still represents Cosby in some civil matters.
Anne Poulin, a law professor at Villanova University, said those involved in the case would probably want to hear from Mr O'Connor "on the theory that, certainly as the lawyer representing Cosby in the civil case, he therefore needed to know what (Cosby's) exposure was to criminal prosecution before he was deposed."
Ms Poulin believes the defence has a high bar to meet to get the case thrown out early on.
At the same time, she said, "if they can win without this ever going to trial, then they've done their client a big service".
Kevin Steele, the new county district attorney, believes Cosby needed an immunity agreement - in writing - to avoid prosecution.
He has said he has no evidence that one exists.
"I never made a deal that involved criminal cases that was not in writing," Lynne Abraham, a longtime judge and district attorney in Philadelphia, said yesterday.
"This is, to me, an extremely unusual arrangement because the prosecutor, Bruce, has made a deal not involving a criminal case, but a civil matter."
The lawyer who served as Mr Castor's top assistant in 2005 could also be called to give evidence.
Risa Vetri Ferman, now a county judge, worked on the Constand case before succeeding Mr Castor as district attorney in 2008.
She reopened the complaint last autumn, asking Mr Castor to submit any documentation of the supposed deal.
Mr Castor pointed to a 2005 press release about his decision not to prosecute Cosby.
Mr Steele defeated Mr Castor in the November election to succeed Ms Ferman.
He believes Cosby needs a written immunity deal to get the case thrown out.
It was not immediately clear when Common Pleas Judge Steven T O'Neill will rule.