This is expected to be one of the biggest trials since OJ Simpson's in 1994-95, except cameras are banned in Pennsylvania courtrooms.
Cosby, 79, is accused of assaulting Andrea Constand, a Temple University basketball official, in January 2004.
She is the former Temple employee, alleging she was drugged and sexually assaulted her in Cosby's suburban Philadelphia home, 13-years ago. If he's found guilty, the fallen star, once nicknamed "America's dad", could spend up to 10 years behind bars.
In what was then a sealed deposition, Cosby acknowledged he had obtained Quaaludes, a sedative, to give them to young women with whom he wanted to have sex.
When Andrea Constand takes the stand in the coming days to break her decade-long silence about Bill Cosby, jurors will hear from a free spirit who devotes her life to family, her French poodle, and her work treating cancer patients and others as a massage therapist.
Constand, who is Canadian, claimed the alleged incident happened when she went to Cosby's mansion in the suburbs of Philadelphia.
The trial will reportedly last for two weeks.More news: Racial slur sprayed on LeBron's house: 'It's tough being black in America'
District Attorney Bruce Castor declined to press charges in 2005, citing insufficient evidence.
According to prosecutors, Cosby told Constand, "These three friends will help you relax", referring to the pills.
Cosby will face a jury of seven men and five women. In the deposition, he said he gave Constand pills that night before putting his hand down her trousers. Instead, Cosby reached a confidential settlement with Constand.
Pulliam previously expressed her support for Cosby during an October 2015 interview with the Today show.
"To be so callous and so remorseless to take advantage of that - to ruin me again - it was like one more nail in my coffin", Valentino said. McMonagle is now joined at the defense table by Angela Agrusa, a Los Angeles lawyer who is also handling at least six lawsuits pending across the country between Cosby and various accusers.
Women began coming forward with accounts of being assaulted by Cosby after comedian Hannibal Buress called Cosby out as a rapist in 2014. He has repeatedly denied the allegations against him, and in an unsealed deposition related to a civil suit filed by Constand, Cosby said the sex was consensual.
Cosby has said he does not plan to testify.More news: Venus Williams out; French Open to have 1st-time Slam champ
She told NBC News she had not seen Cosby since then, and came forward along with dozens of other women in recent years.
Allred represents several of Cosby's accusers, including a woman who worked for the comedian's agent at the William Morris agency.
McMonagle, alternating between an intimate whisper and a window-rattling voice of doom, issued a scathing assessment of Constand, saying that she had been "untruthful time and time and time again".
The district attorney at the time of the alleged assault declined to press charges, and in 2006 Cosby settled a civil suit with Constand that remained sealed for nearly a decade.
Cosby's lawyers have spent the past 18 months trying to have the criminal case thrown out.
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.More news: Golden State Warriors: Three stars after Game 2 victory over Cavaliers
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