Bill Cosby arrives for Day 6 of his sex-assault retrial, April 16, 2018, in Norristown, Pa.
Matt Slocum, AP

Bill Cosby's chief accuser underwent further grilling Monday by defense lawyers looking to portray her as a vengeful unrequited lover to raise doubts about her credibility and motives on Day 6 of the comedian's sexual-assault retrial in suburban Philadelphia. 

The latest developments:

Accuser's mother takes the stand

Andrea Constand's mother, Gianna Constand, took the stand Monday at Cosby's sexual-assault retrial to testify for the prosecution that Cosby described to her a sexual encounter with her daughter and apologized for his behavior.

Gianna Constand, who also testified at Cosby's first trial and who taped some of her phone conversations with Cosby more than a decade ago, said she called the comedian to ask him about the medication he'd given her daughter and what he'd done to her.

She says Cosby told her he gave Andrea Constand a prescription drug but didn't give her the name. Gianna Constand said she called him because her daughter hadn't been the same since leaving Temple University in Philadelphia in March 2004, about two months after the alleged assault, and moving back to her mother's house in her native Canada.

Gianna Constand, mother of Andrea Constand, after testifying at Bill Cosby's sex-assault retrial in Norristown, Pa. on April 16, 2018.
DOMINICK REUTER, AFP/Getty Images

Gianna Constand said Cosby admitted to her that he was a "sick man," and that he "felt like a dirty old perverted man."

Accuser denies framing Cosby or knowing key defense witness

Gianna Constand was called after her daughter left the witness stand Monday afternoon following hours of pointed questioning over two days, during which she denied framing Cosby. She also insisted she doesn't know a key defense witness who plans to testify that she spoke of making false accusations against a celebrity to make money.

Cosby's lead attorney, Tom Mesereau, concluded his initial cross-examination by asking Constand: "Did you ever fabricate a scheme to falsely accuse him for money?"

"No sir," Constand replied.

Constand also denied knowing or having a conversation with Marguerite Jackson, a former Temple University colleague. The defense plans to call Jackson to testify about how Constand allegedly talked to her about a plan to set up a high-profile person and file a lawsuit to extract money from him.

That testimony is part of the defense strategy to attack Constand's credibility and portray her as a greedy "con artist" who falsely accused Cosby for money.  

Jackson, who claims she and Constand were friends and had shared hotel rooms several times, was blocked from testifying at the first trial after Constand denied knowing her. Later, Constand remembered she knew a woman named "Margo." Judge Steven O'Neill ruled that Jackson can take the stand at the retrial but said he might revisit the issue after Constand finished testifying.

On Monday, Constand again denied knowing Jackson. 

What was the accuser's relationship with Cosby?

Constand, 45, who endured hours of pointed cross-examination by Mesereau on Friday, went back on the witness stand Monday to be confronted by more questions about her relationship with Cosby.

She acknowledged spending 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 she says he drugged and molested her in 2004, jurors learned Monday as the defense sought to undermine her account.

Constand said that her phone calls to Cosby were about basketball and had nothing to do with romance. 

Constand says Cosby drugged and sexually assaulted her at his home; he says he gave her an over-the-counter cold medication and their encounter was consensual.

He has been charged with three counts of aggravated indecent assault; a conviction on any of the charges could get him 10 years in prison.

Cosby arrived at the rain-soaked suburban Philadelphia courthouse on Monday morning wearing a black raincoat and walking under a large, black umbrella held by his spokesman, Andrew Wyatt.

Meanwhile, Judge O'Neill, who also presided over Cosby's first trial, disclosed that the emergency surgery he had over the weekend to repair a torn retina in his left eye was successful. He said he was relieved doctors were able to perform the laser procedure before permanent damage to his eye set in, and without delaying the trial or keeping sequestered jurors cooped up in their hotel longer.  

Judge Steven O'Neill, who is presiding over Bill Cosby's sex-assault retrial in Norristown, Pa., on April 10, 2018.
Pool

Defense tries to raise doubts about accuser's testimony

Picking up where he left off Friday, Mesereau questioned Constand about inconsistencies in her police statements and prior testimony, and about the nature and extent of her relationship with Cosby.

Mesereau said Constand told police in 2005 that she called Cosby from her university-issued cellphone just before she arrived at his house on the night of the alleged assault to ensure the gate would be open. But Constand's phone records show she did not make any calls to Cosby's home that month.

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.

Mesereau is trying to persuade the jury to see Constand as an unrequited lover who acted inappropriately by showing interest in the long-married Cosby. She maintains she viewed Cosby as a mentor and never had a romantic interest in him.

Phone records show Constand, the former director of women's basketball operations at Temple University, made brief calls to Cosby around the time of a Temple home game on Feb. 14, 2004, the month after the alleged assault. 

"You think you called Mr. Cosby to talk about basketball?" Mesereau asked her.  Constand testified that she felt a duty to answer Cosby's inquiries since he was a powerful alumnus and trustee. 

Mesereau asked Constand why she went to a married man’s hotel room when she went to see him perform in Connecticut months before the alleged assault. Constand said Cosby asked her to "come pick up baked goods...I didn't know I was going to be going into his room.”

Cosby's first trial last June

More: Bill Cosby retrial, Day 5: Chief accuser Andrea Constand grilled by defense on discrepancies in her story

More: Bill Cosby retrial, Day 4: Final additional accuser testifies she trusted 'America's Dad'

Andrea Constand, Bill Cosby's main accuser at his sex-assault retrial, headed back to witness stand on Day 6 for more cross-examination.
DOMINICK REUTER, AFP/Getty Images

More: Bill Cosby's retrial: What you need to know before opening statements

More: Bill Cosby retrial, Day 1: Prosecutor says Cosby paid accuser nearly $3.4 million in 2006

Contributing: The Associated Press