Canadian Andrea Constand told jurors she doesn't "recall ever having a conversation with" Marguerite Jackson.
The comments came on the second day of testimony for Constand, the former Temple University employee who testified that Cosby acted as a mentor to her, gained her trust, and then drugged and sexually assaulted her in 2004. Jackson has said that she and Constand worked closely together, had been friends and had shared hotel rooms several times.
Gianna Constand, who testified during Cosby's first trial on the same charges, brought new emotion to the courtroom as she rehashed her disturbing communications with the TV pioneer. At the time, Judge Steven O'Neill ruled Jackson's testimony would be hearsay.
"It did not state that she could not cooperate, that is speak to investigators, if there were a criminal investigation", Attorney Gloria Allred said.
Gianna testified she noticed Andrea was not the same after leaving her job at Temple.
Cosby lawyer Tom Mesereau, who has called Constand a "con artist" who framed Cosby and then collected a $3.4-million settlement, asked her about Jackson during cross-examination on Monday.
A judge blocked Jackson from testifying at last year's trial after Constand took the stand and denied knowing her.
Constand said she didn't remember taking a required sexual assault and harassment training seminar when she started working at Temple, or another one on avoiding conflicts of interest, such as fraternizing with board trustees.
The entertainer came under fire past year during his first trial by openly leering as Constand fully recounted, in graphic detail, her memory of the alleged assault.
Andrea Constand is one of about 50 women who have accused Cosby of assaults dating back decades, accusations that he denies. After she consumed three blue pills that he said would relax her, she said she became immobilized and awoke to find Cosby touching her breasts and vagina and using her hand to stroke his penis.
"When I was talking to him my anger was so fierce, I had broken capillaries in my eyes and my eyes were like two pools of blood", Constand, who traveled from Ontario, Canada to testify, said of the January 2005 phone call.
Cosby paid Constand $3.38 million to settle a civil suit that Constand filed after Pennsylvania prosecutors in 2005 initially declined to charge Cosby for the alleged assault. The defence said she spent late nights at the comedian's home, drove four hours to see him at a casino and called him twice on Valentine's Day, about a month after the alleged assault. And she said her phone calls to Cosby were about basketball and had nothing to do with romance.
She told jurors that Cosby said he "felt like a dirty old perverted man" and, at the end of the call, conceded he was a "sick man".
Mesereau, in his cross-examination of Constand, asked her about inconsistencies in her statements to police about the alleged assault.
Constand denied telling a defense witness almost 13 years ago she was hatching a plot to extort money from a celebrity, but Constand went even further than that, denying that she even knew Marguerite Jackson.
The defence pointed to the phone records as evidence that she had kept in touch with Cosby in the following weeks at a level at odds with her account of having been assaulted.
Constand explained that she may have been mistaken, that there were times Cosby told her in advance that the gate would be open and that she often reached him at another number.
Five other women who also allege that Cosby drugged and assaulted them were called to the stand by the prosecution. The defence has called the other accusers irrelevant to the case.