"We cannot come to a unanimous consensus on any of the counts," the jury said in a note to Judge Steven O'Neill in Norristown, Pennsylvania. Jurors began discussing the three counts of aggravated indecent assault late on Monday and worked 12-hour days on both Tuesday and Wednesday.
In response, O'Neill gave a standard instruction that the jurors should continue trying to reach a verdict without compromising any of their individual beliefs.
As reporters streamed out of the courtroom, poet and author Jewel Allison - one of the dozens of women who have accused Cosby of assaulting them - burst into tears. Several of the accusers have been in court all week awaiting a verdict, including the woman at the center of the trial, Andrea Constand.
Cosby, the 79-year-old entertainer once beloved for his brand of family-friendly comedy, is accused of drugging and sexually assaulting Constand, then 31, at his home near Philadelphia in 2004.
Constand's allegations are the only ones to result in criminal charges, with many of the others too old to allow for prosecution. Cosby has denied every claim, saying his encounters with Constand and others were consensual.
A hung jury would be a clear victory for Cosby, who would avoid what could have been years in prison. Prosecutors would have the option of seeking a retrial if the jury cannot reach a verdict.
On hearing of the jury's note, his lawyers moved for a mistrial. But O'Neill denied that request as premature.
Cosby's spokesman, Andrew Wyatt, told reporters outside the courthouse that the jurors understand "the facts of this case don't add up."
But Gloria Allred, a high-profile lawyer who represents more than 30 Cosby accusers, said the jury's note was not vindication for the entertainer.
"It's not over until it's over, and it's not over yet," she said.
The jury also revisited Cosby's description of the night from sworn depositions he gave in 2005 and 2006 during a civil lawsuit by Constand and a police interview he conducted in 2005. Cosby did not testify.
Defense lawyers during the trial emphasized discrepancies in Constand's statements to police in 2005 in an effort to undermine her credibility.
Prosecutors, meanwhile, used her testimony as well as the words of a second accuser, Kelly Johnson, to portray Cosby as a serial predator. Johnson told jurors Cosby sexually assaulted her in strikingly similar fashion in 1996.
In his decade-old depositions, Cosby said he gave Constand Benadryl, a common allergy drug whose side effects can include drowsiness. He called the pills her "friends" without telling her what they were, and admitted to giving other young women Quaaludes, a sedative, in the 1970s.