Bill Cosby's trial on sexual assault charges has ended in a mistrial after jurors failed to reach a unanimous decision in a case that nevertheless helped destroy the 79-year-old comedian's image as "America's Dad."

Prosecutors vowed to try again, declaring the woman who accuses Cosby of drugging and molesting her at his Philadelphia-area home in 2004 is "entitled to a verdict."

The jury deliberated more than 52 hours over six days before telling a judge they couldn't agree on whether The Cosby Show star sexually violated Temple University employee Andrea Constand after giving her pills that left her unable to say no or fight back.

The judge then declared a mistrial.

Cosby's team declared victory and went on the attack.

"Mr. Cosby's power is back. It has been restored," said Andrew Wyatt, his spokesman.

Cosby's wife of 53 years, Camille, slammed prosecutors for bringing the case to court, calling District Attorney Kevin Steele "heinously and exploitively ambitious" in a statement released after court adjourned.

She also attacked the judge, the accuser's lawyers and the media.

"How do I describe the judge? Overtly arrogant, collaborating with the district attorney," said her statement, which was read by Wyatt.

Cosby himself didn't comment. He remained stoic as the judge declared a mistrial, while Constand doled out hugs to her mother, prosecutors and some of the other women who say the TV star drugged and abused them.

Steele said he's disappointed the jury was unable to agree on the charges, but vowed to put Cosby on trial again.

Constand "has shown such courage through this, and we are in awe of what she has done," Steele said. "She's entitled to a verdict in this case."

Cosby's career and good-guy image were already in tatters by the time his chief accuser took the stand and described how Cosby gave her pills and then sexually assaulted her as she lay paralysed on a couch, unable to tell him to stop.

But the jurors clearly struggled with their verdict, telling the judge on Day 4 they were at impasse.
Judge Steven O'Neill instructed them to keep working toward a unanimous decision.

On Saturday, they came back and told O'Neill they were hopelessly deadlocked.

It was the only criminal case to arise from allegations from more than 60 women that cast Cosby as a serial predator who gave drugs to women before violating them.

He did not take the stand in his own defence, leaving it to his attorney to argue Cosby and Constand were lovers sharing a consensual sexual encounter. Lawyer Brian McMonagle told jurors that while Cosby had been unfaithful to his wife, he didn't commit a crime.

Cosby broke barriers as the first black actor to star in a network show, I Spy, in the 1960s and created the top-ranked Cosby Show two decades later, starring as kindly Dr. Cliff Huxtable.

Before going on trial, Cosby expressed hope he could eventually resume his career. But TV networks had long since scrapped plans for a comeback and pulled reruns from the air.