Why Bill Cosby’s sexual assault conviction has been overturned by Pennsylvania’s highest court

ITV News US Correspondent Emma Murphy reports on Bill Cosby's overturned conviction

Bill Cosby's sexual assault conviction has been overturned by Pennsylvania’s highest court over a technicality.

The ruling freed the actor - once known as "America's Dad" - from prison on Wednesday as the court found an agreement with a previous prosecutor, which prevented him from being charged in the case.

The 83-year-old comedian was convicted in 2018 for drugging and molesting Andrea Constand, a Temple University employee at his mansion in Philadelphia.

He has spent more than two years of a three-to-10-year sentence at a state prison near Philadelphia.

Cosby was the first celebrity tried and convicted in the #MeToo era, and his conviction was seen as a turning point in the movement to hold powerful men accountable for sexual misconduct.

Bill Cosby arrives home in Elkins Park, Pennsylvania, on Wednesday afternoon, shortly after his release from prison

So why did the highest court in Pennsylvania overturn his conviction?

The split court found Cosby was unfairly prosecuted because the previous district attorney had promised the comedian he wouldn't be charged over Constand’s accusations.

However, Cosby was charged by another prosecutor who claimed he wasn't bound by that agreement.

The court said that's not the case, as the justices found Cosby relied on this promise when he agreed to testify without invoking his Fifth Amendment right against self-incrimination in a lawsuit brought against him by Constand.

The court concluded the prosecutor who later brought the charges was obligated to stick to the non-prosecution agreement, so the conviction cannot stand.

The justices wrote "denying the defendant the benefit of that decision is an affront to fundamental fairness, particularly when it results in a criminal prosecution that was foregone for more than a decade."

ITV News US Correspondent Emma Murphy explains why Pennsylvania's Supreme Court saw Bill Cosby's conviction at fault

What is a non-prosecution agreement and why is it relevant to Cosby?

The promise not to prosecute Cosby was made in 2005 by Bruce Castor, who was then the top prosecutor for Montgomery County.

Castor was also on the legal team that defended former President Donald Trump during his historic second impeachment trial over the January 6 insurrection at the U.S. Capitol by his supporters.

During a court hearing, weeks after Cosby’s 2015 arrest, Castor testified that he promised Cosby he wouldn’t be prosecuted in the hope it would persuade the actor to testify in a civil case brought by Constand and allow her to win damages.

Castor acknowledged the only place the matter was put in writing was in the 2005 press release announcing his decision not to prosecute, but said his decision was meant to shield Cosby from prosecution "for all time."

However his successor noted, during the appeal arguments, Castor later said in the press release he could revisit the decision in the future.

Castor had said Constand’s case would be difficult to prove in court because she waited a year to come forward and stayed in contact with Cosby.

The first jurors who heard the case may have agreed with him, as they could not reach a verdict in 2017.

But a second jury empanelled after the #MeToo movement exploded found him guilty at his 2018 retrial. Constand settled her civil case against Cosby for more than £2,170,815 ($3 million).

Castor’s successor, District Attorney Kevin Steele, charged Cosby in 2015 after a federal judge unsealed documents from her 2005 lawsuit against Cosby, revealing his damaging testimony about sexual encounters with Constand and others.

Castor has said Cosby "would’ve had to have been nuts to say those things if there was any chance he could’ve been prosecuted."

Has this happened before?

Wesley Oliver, a Pennsylvania law professor who has followed Cosby’s case closely over the years, said he has never heard of a high court in Pennsylvania or anywhere else grappling with a prosecutor’s informal promise not to prosecute.

"It breaks new ground entirely," said Oliver, who teaches at Duquesne University School of Law in Pittsburgh.

"It sets precedent not just for Pennsylvania but probably other states," he added.

He said the ruling should drive home to prosecutors the risks of suggesting at news conferences, in press releases or verbally in private they will not prosecute.

"They should at least add three words - 'at this time'," he said.

"If you add that qualifier, which wasn’t done in Cosby’s case, you should be good to go," Oliver said.

Can Cosby go to court again?

It's highly unlikely. The decision on Wednesday bars Cosby from being tried again over Constand’s complaint, finding it to be the "only remedy that comports with society’s reasonable expectations of its elected prosecutors and our criminal justice system."

The accusations raised by dozens of other women, including the five who testified at his 2018 trial, often go back decades and are most likely too remote to prosecute.

Cosby turns 84 next month. However, his lawyer said he remains in good health, except for vision problems which make him legally blind.