Cosby is charged with three counts of aggravated indecent assault. He could get 10 years in prison if convicted.
The TV star carried a wooden cane and grabbed his spokesman's arm for support as he walked past dozens of cameras into the courthouse. Cosby's wife, Camille, was not in court. But actress Keshia Knight Pulliam, who played his daughter Rudy on the top-rated Cosby Show in the 1980s and '90s, was at his side as he made his way into the building.
Cosby smiled but said nothing when someone asked how he was feeling.
Pulliam told reporters she came to the trial to support her TV dad.
"I want to be the person that I would like to have if the tables were turned," she said. "Right now it's the jury's job and the jury's decision to determine guilt or innocence. It's not mine or anyone else's."
Constand, 44, of the Toronto area, is expected to take the stand this week and tell her story in public for the first time. A woman who claims Cosby drugged and assaulted her in 1996 will also testify in an effort by prosecutors to show that he had pattern of behavior.
Cosby built a good-guy reputation as a father and family man, on screen and off, during his extraordinary 50-year career in entertainment. He created TV characters, most notably Dr. Cliff Huxtable, with crossover appeal among blacks and whites alike. His TV shows, movies and comedy tours earned him an estimated $400 million.
Then a deposition unsealed in 2015 in a lawsuit brought by Constand revealed that Cosby had a long history of extramarital liaisons with young women and that he obtained quaaludes in the 1970s to give to women before sex. Dozens of women soon came forward to say he had drugged and assaulted them.
The statute of limitations for prosecuting Cosby had run out in nearly every case. This is the only one to result in criminal charges against the comic.
Feden told jurors that celebrities like Cosby are seen as "larger than life."
"We think we really know them," she said. "In reality, we only have a glimpse of who they really are."
Prosecutors had wanted to call as many as 13 of Cosby's more than 60 accusers as witnesses, but Montgomery County Judge Steven O'Neill ruled that only Constand and the other woman could take the stand.
Celebrity attorney Gloria Allred, who showed up for the first day of the trial, told reporters she is hopeful "there will be justice in this case."
Allred represents several of Cosby's accusers, including the one who will testify for the prosecution — a woman who worked for the comedian's agent at the William Morris agency.
"This case is not going to be decided on optics," Allred said. "It's going to be decided on the evidence, and finally, it's Mr. Cosby who's going to have to face that evidence and confront the accusers who are against him."
Constand filed a police complaint in 2005 over the encounter at Cosby's home. The district attorney at the time said the case was too weak to prosecute. But a new set of prosecutors charged Cosby a year and a half ago after the deposition became public and numerous women came forward.
On Monday, McMonagle suggested Constand and the other accuser set to testify were seeking payouts over the allegations. And he told jurors that Cosby apologized to Constand's mother in a phone call the year after the encounter not because he had assaulted her, but to say, "I'm sorry, I'm a married man, and I never should have done it."
Cosby's lawyers tried repeatedly to get the case thrown out. They said Cosby testified in the lawsuit only after being promised he could never be charged. And they argued that the delayed prosecution makes the case impossible to defend, given that witnesses have died, memories have faded and Cosby, they say, is blind.
The AP does not typically identify people who say they are sexual assault victims unless they grant permission, which Constand has done.
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