NORRISTOWN, Pa. — Bill Cosby went on trial Monday on charges he drugged and sexually assaulted a woman more than a decade ago, with prosecutors immediately introducing evidence that the 79-year-old TV star once known as America’s Dad had done it before to someone else.
The prosecution’s opening witness was not the person Cosby is charged with abusing, but another woman, who broke down in tears as she testified that the comedian violated her in the mid-1990s at a hotel bungalow in Los Angeles.
Cosby is on trial on charges he assaulted Andrea Constand, a former employee of Temple University’s basketball program, at his suburban Philadelphia mansion in 2004. His good-guy reputation already in ruins, he could get 10 years in prison if convicted.
In her opening statement, prosecutor Kristen Feden noted that “The Cosby Show’’ star previously admitted under oath that he gave Constand pills and touched her genitals as she lay on his couch.
‘‘She couldn’t say no,’’ Feden said. ‘‘She can’t move, she can’t talk. Completely paralyzed. Frozen. Lifeless.’’
Cosby attorney Brian McMonagle countered by attacking what he said were inconsistencies in Constand’s story, disputed that Constand was incapacitated, and made the case that she and Cosby had a romantic relationship.
He said Constand initially told police that she and Cosby did not speak after their 2004 encounter, when, in fact, phone records show the two talked 72 times after mid-January — with 53 of those calls initiated by Constand.
Constand, 44, of the Toronto area, is expected to take the stand this week and tell her story in public for the first time.
The trial’s first witness was Kelly Johnson of Atlanta, who worked for one of Cosby’s agents at the William Morris Agency. She described an encounter she said took place in 1996 at the Hotel Bel-Air when she was in her mid-30s.
Prosecutors are trying to show Cosby’s treatment of Constand fit a pattern of predatory behavior.
They had wanted to call as many as 13 women who say Cosby sexually assaulted them, out of more than 60 accusers in all. But Judge Steven O’Neill, in a victory for Cosby, said the jury could hear only from Constand and Johnson.
Johnson testified that Cosby pressured her to take a large white pill that knocked her out, and when she woke up he put lotion on her hand and forced her to touch his genitals.
‘‘My dress was pulled up from the bottom, and it was pulled down from the top, and my breasts were out,’’ she said, crying. ‘‘And I felt naked.’’
Cosby’s lawyer argued that Johnson was seeking a payout from the TV star.
McMonagle said Johnson mixed up the years and other details of her encounters with Cosby, and he grilled her about why she never said anything when she left William Morris. She came forward in 2015 at a news conference with celebrity lawyer Gloria Allred.
‘‘I felt embarrassed because I had a secret about the biggest celebrity in the world at the time and it was just me, just my word against his, and I was very afraid,’’ Johnson said.
Cosby grinned and tapped his wooden cane as his lawyer questioned Johnson.
The comedian arrived at the courthouse in the morning holding his spokesman’s arm for support as he walked past dozens of cameras.
Cosby’s wife, Camille, was not in court. But actress Keshia Knight Pulliam, who played his daughter Rudy on ‘‘The Cosby Show’’ in the 1980s and ’90s, was at his side as he made his way into the building. She told reporters she was there to support her TV dad.
Cosby built a wholesome reputation as a father and family man, on screen and off, during his extraordinary 50-year career in entertainment. 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 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.
Those developments led prosecutors in Pennsylvania to bring charges against Cosby a decade after the district attorney at the time concluded the case was too weak.
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.