"We're going to retry the case", said Montgomery County District Attorney Kevin Steele.
Ms Constand, who was then 31, said he had offered her unidentified pills one night that left unable to stop his advances.
Outside the courthouse, as Cosby stood silently behind them, members of his team criticised the case against him.
"The jurors used their power to speak, and Mr. Cosby's power is back", Wyatt said after leaving the courthouse.
California: Cosby is being sued in Los Angeles by Judy Huth, who accuses the comedian of forcing her to perform a sex act on him in a bedroom of the Playboy Mansion around 1974, when she was 15. Cosby pleaded not guilty to three charges of aggravated indecent assault.
"They really put their heart and soul into it", she said.
Allred said she believes that justice will prevail.
Troiani acknowledged the difficulty of the case, given the passage of time and the impact of the alleged drugging on Constand's ability to recall details.
Legal experts say prosecutors in Bill Cosby's sexual assault case are likely to reshape their case for the second trial. Time will tell whether prosecutors will bring another case against the famed TV comedian.
Massachusetts: Seven women are suing Cosby for defamation in separate lawsuits pending in Massachusetts, where Cosby has a home in Shelburne Falls.More news: Zach Johnson making an early move at Erin Hills
In a written statement, Cosby's wife Camille attacked the district attorney and the news media for their handling of the sexual assault allegations, which brought down one of America's most popular figures. She also denied that the two had had a romantic relationship prior to that encounter.
She condemned the district attorney as "heinously and exploitatively ambitious", the judge as "overtly arrogant", lawyers for the accusers as "totally unethical" and "many" in the media as "blatantly vicious".
But after 12 jurors became deadlocked in their deliberations, a Pennsylvania judge declared the case a mistrial. "It has been restored".
The prosecution said they were pursuing a fresh trial. He also found success with his "Fat Albert" animated TV show and starred in commercials for Jell-O pudding. He still faces at least four civil lawsuits from at least 10 accusers.
Three of the questions were requests to review what Cosby said and another two were about the testimony of his accuser, Andrea Constand. He says he gives her drugs.
He added that jurors should be proud of how they handled the case even though they could not reach a unanimous verdict. "We, the jury, are deadlocked on all counts", said the note read by O'Neill on Saturday morning.
It wasn't immediately known how many jurors wanted to convict and how many wanted to acquit.
The jury deliberated for 54 hours; longer than the trial itself. #CosbyTrial. Heart goes out to women who came forward.
He was eventually charged in December 2015, just days before the statute of limitations was set to expire.