GEOFF BENNETT: When the organization Centurion was founded some 40 years ago, it was the first group of its kind working to overturn wrongful convictions for people facing execution or life sentences.

Decades later, as the death penalty continues to be carried out in some states and debated in others, its work continues, a story now told by its founder and one of today's most popular novelists.

Senior arts correspondent Jeffrey Brown reports for our series Art in Action, exploring the intersection of art and democracy, part of our Canvas arts and culture coverage.

(CHEERING) JEFFREY BROWN: In 2021, Larry Walker left a Pennsylvania state prison a free man after serving 38 years following a conviction for murder.

On this day, he was visiting friends at Centurion, the Princeton, New Jersey, group that took on his case and finally convinced a judge and even Walker's trial prosecutor that his conviction had been based on the weakest of evidence and a flawed defense.

LARRY WALKER, Wrongfully Convicted: I have always heard that happens to other people, but when it had happened to me, reality just set in.

But I don't know, exactly when I look back, how this happened.

In the new book "Framed: Astonishing True Stories of Wrongful Convictions," Centurion's founder, Jim McCloskey, and bestselling novelist John Grisham show how it happened in 10 separate harrowing cases.

JIM MCCLOSKEY, Author, "Framed: Astonishing True Stories of Wrongful Convictions": We want to educate the public and those who administer the criminal justice system that this kind of thing, wrongful convictions, is far more common than you would ever believe.

JOHN GRISHAM, Author, "Framed: Astonishing True Stories of Wrongful Convictions": It's a huge problem we have.

People don't believe that these cases happen.

They don't believe there are thousands of innocent people in prison.

So we said, OK... (CROSSTALK) JEFFREY BROWN: Because it just feels impossible.

JOHN GRISHAM: They trust the system.

JEFFREY BROWN: In their book and in public appearances, as here at Princeton's Nassau Presbyterian Church, they offer case studies of men and women, black and white, failed by the system, while also relating their own paths to a personal commitment to help others, how at age 38, after working in the business world but wanting more meaning in his life, Jim McCloskey entered Princeton Theological Seminary and served as a student chaplain at Trenton State Prison, where he met Jorge de los Santos, who insisted on his innocence.

JIM MCCLOSKEY: After months and months of talking to him about his case, reading his transcripts, he asked me a question after Thanksgiving of 1980.

He said: "Jim, do you believe I'm innocent?"

I said: "Yes, I believe you're innocent."

Then he said: "Well, what are you going to do about it?

What are you going to do?

Go back to your nice little seminary in Princeton and pray for me?

That's not going to get me out."

So he challenged my faith.

He really shook me up.

JEFFREY BROWN: That challenge would grow into Centurion, where volunteers pore through old court filings and correspond with inmates before any decision is made to take on a case.

And staff members work to help people post-release.

WOMAN: So your brother couldn't use any help on his food truck or anything like that?

JEFFREY BROWN: To date, Centurion has won the freedom of some 71 people, now led by executive director Corey Waldron, working through old-fashioned, on-the-street reinvestigations of old cases, often 20 years after a conviction, mostly without available DNA tests, looking for new or missed evidence or misconduct by police, prosecutors or courts.

John Grisham took a different path.

He'd been a young lawyer and state representative in Mississippi before turning to fiction, with thrillers from "A Time to Kill" and "The Firm" up to this year's "Camino Ghosts," some 51 books, many turned into films, that have sold more than 300 million copies.

His early experience as a lawyer led him to believe the system did work, until he came upon a 2004 obituary of a man named Ron Williamson, who spent 11 years on death row and came within days of being executed before DNA evidence cleared him.

The story of how that happened became Grisham's first nonfiction book, "The Innocent Man."

JOHN GRISHAM: There was a shock at every turn.

Every time I researched that case, which was for 18 months, I found something new every day that I just -- I couldn't believe.

But that case took me into the world of wrongful convictions, something I had never thought about before.

And once I got there, I'm still there.

JEFFREY BROWN: Every case of wrongful conviction has its own details, its own twists and turns.

But John Grisham and Jim McCloskey, who retired in 2015, see routine patterns, including evidence tampering, coerced interrogations that lead to false confessions, an overreliance on untrustworthy witnesses and junk science and racial bias.

Each chose and wrote of five cases.

There have been questions in the media about Grisham's overuse of reporting and language of others without sufficient attribution in the new book.

In response, he cites eight pages of footnotes and citations and stands by his work.

The book delves into the legal nuts and bolts and narrative drama of each case.

McCloskey says the real crime, malfeasance, is plain to see.

JIM MCCLOSKEY: They're astounding, the ineptness and the corruption in how the police and the prosecutors went after completely innocent people who had no criminal records, were clean as a houndstooth, and how they just with zeal went after it to either send them to death row or send them away to prison for life for crimes they had absolutely nothing to do with.

LARRY WALKER: I think we can take our names off today what is still many men and women that are in prison.

JEFFREY BROWN: Larry Walker was fortunate in one way.

He had the support of friends and family.

But, in 1983, his murder conviction was largely based on the testimony of two witnesses.

Another witness said Walker was not among the three men she'd seen fleeing the attack.

But police never identified other suspects.

Over years of work on the case, Centurion staff led by legal director Paul Casteleiro and investigator Alan Maimon, documented the narrow investigation, shoddy defense Walker received and other factors, leading the current Philadelphia district attorney's office to agree that a troubling confluence of circumstances had led to Walker's arrest and conviction.

They called for his release, and a judge agreed.

And Walker was freed in 2021.

His daughter Sharena and he say they sought for years to get lawyers, the courts, anyone to hear and help him, until Centurion took his case in 2012.

LARRY WALKER: As time went on, my faith and my hope, it was getting less, until Centurion eventually accepted my case.

And then I had my faith and hope grow.

SHARENA ROBINSON, Daughter of Larry Walker: I felt like we hit the lottery.

JEFFREY BROWN: The lottery, yes.

SHARENA ROBINSON: Oh, my gosh.

JEFFREY BROWN: Because, before that... SHARENA ROBINSON: It was -- I mean, I'm 44, and at the time I was only 2.5 when my father was falsely convicted of a crime he didn't commit.

So, of course, as time goes on, the case gets older, so evidence can possibly get lost, or misplaced, whatever the case may be.

And it was like -- it was no hope.

So, they gave us hope.

They gave us hope.

They gave us my father.

They brought him home, because it was, without them, we wouldn't have been here.

JEFFREY BROWN: So, Larry, 38 years of your life.

Are you bitter?

LARRY WALKER: I'm bitter because of what was taken from my family, from my son and daughter, and my mother, and my father.

I'm not bitter.

I'm just not bitter because I have faith that things happen for a reason.

I'm just really more thankful than to be bitter.

JEFFREY BROWN: Grisham says every wrongful conviction case deserves a book of its own.

JOHN GRISHAM: The elements are there for great storytelling.

There's great drama, injustice, corruption, loss, perseverance, maybe redemption, maybe not.

But elements go into the stories that are just gravy for a writer.

JEFFREY BROWN: These cases matter profoundly for the individuals involved and their families and friends.

But McCloskey and Grisham make a larger case, why it should matter to us all, going to the heart of how democracy works or doesn't.

JIM MCCLOSKEY: I would think the public and the world wants to know how accurate its criminal justice system is.

And if it's flawed, then let's lay it out on the table and point out its flaws and its deficiencies, because the last thing in the world anybody wants, regardless of their political affiliation, is for an innocent person to be wrongly convicted and sentenced to death or to life.

Who would want that?

Who would be proud of that?

JOHN GRISHAM: You know, our democracy is based on the rule of law.

You can't have a criminal justice system that's grossly unfair, that convicts innocent people and turns the other eye to guilty people.

If that happens, and it does happen, if it happens too often, then the whole rule of law starts to crumble.

And it's the cornerstone of our democracy.

JEFFREY BROWN: For the "PBS News Hour," I'm Jeffrey Brown in Princeton, New Jersey.