For the retrial, a judge has ruled that jurors can hear from five additional accusers, giving prosecutors a chance to portray the man once known as "America's Dad" as a serial predator.
Judge Steven O'Neill said the defence can call a witness who says Cosby's accuser talked about framing a celebrity before she lodged sexual abuse allegations against Cosby in 2005.
Jackson's testimony was crucial to a defence plan to portray Constand as a greedy liar.
A juror who spoke to The Associated Press on condition of anonymity said he was suspicious of Constand's story, questioning why she waited to tell authorities about the alleged assault and suggesting the clothing she wore to Cosby's house had influenced his view of their encounter.
O'Neill ruled that Marguerite Jackson could take the witness stand after he blocked her from testifying at the first trial ‚ which ended in a hung jury ‚ saying her testimony would be hearsay.
More than half of the 120 potential jurors being questioned ahead of Bill Cosby's sexual assault retrial say they have already formed an opinion about the comedian's guilt or innocence.
The ruling to allow Margo Jackson's testimony came on the second day of jury selection for the second trial where the 80-year-old entertainer will face charges that he sexually assaulted a staffer more than a decade ago at his alma mater, Temple University in Philadelphia.
The judge presiding over Bill Cosby's felony sexual-assault trial handed the defense a big win today.
Jury selection for the retrial got under way on Monday, with all but 10 potential jurors indicating they have knowledge about the case.
Veteran lawyers and jury consultants say #MeToo could cut both ways for Cosby, making some potential jurors more hostile and others more likely to think men are being unfairly accused. The panel so far has four men and three women.More news: Intel Core i9 is the most advanced processor for laptops today
Just one juror was seated as jury selection began on Monday.
Constand said that in 2004 she went to Cosby's home in Philadelphia and that he drugged and molested her when she was unconscious.
Prosecutors and the defence have begun the hard task of picking a jury for Bill Cosby's sexual assault retrial today.
What happened in the first trial: Constand testified, Cosby did not. Almost everyone else in the initial jury pool of 120 suburban Philadelphia residents indicated they knew about the charges against Cosby - including the two women picked Tuesday - and scores of potential jurors were sent home because they said they'd already formed an opinion about the former TV star's guilt or innocence.
The jury questioning revealed some potential witnesses, including Dawn Staley, the SC women's basketball coach who was Ms Constand's boss at Temple, Temple board President Patrick O'Connor, who represented Cosby in Ms Constand's 2005-06 lawsuit against him, and Judge Risa Vetri Ferman, the former district attorney who charged Cosby just before she left office in 2015.
Rather than raise their juror numbers at the same time to give an affirmative answer, as they did for other questions, he asked them to raise their numbers row by row.
A new group of potential jurors summoned to Bill Cosby's sexual assault retrial is proving more opinionated and less willing to serve than the panel that produced seven jurors over the last two days.
All but one potential juror say they have heard or seen something about the #MeToo movement exposing sexual misconduct in the entertainment industry. The lone person who claimed ignorance on #MeToo was not invited back.
"Since Cosby's first go-round, all courtroom participants - jurors, attorneys, judge - have been immersed in an intensive course on sexual violation", Ms Deborah Tuerkheimer, a law professor at Northwestern University said, "including the kind of sexual assault inflicted by mentors".
Prosecutors and the defense agreed to strike 89 potential jurors out of an initial pool of 120. He also ruled that the jury can hear the amount of the settlement that Cosby reached with his accuser.