In our last episode, we met Andrew Wilson, a man imprisoned for 32 years for crimes he did not commit.

Evidence that could have freed him was withheld.

Andrew's lawyer was Paula Mitchell.

Paula now heads the Los Angeles Innocence Project.

Some years ago, when I became aware of the Innocence Project, I was like, okay, we're good because we have science on our side, and so everybody's whose Innocent is going to be exonerated.

But that's not true.

Law enforcement and the prosecution will have information-- interviewing witnesses, looking at evidence, and they have their working theory of the case.

This witness doesn't matter.

That's not material.

That's not exculpatory.

I don't have to give that to the defense.

I'm talking about the cases I've worked on ten, 20, 30, 40 years ago.

All of a sudden, all this stuff that was never disclosed is highly material.

And oftentimes that is where the truth lies.

It's absolutely stunning.

It's heartbreaking.

People who are responsible for suppressing evidence or committing misconduct go on and get promoted.

And once you bound over for trial, the pressure to plead guilty to something you didn't do starts to get really intense.

Prosecutor offices across the country, some have started what they call conviction integrity units, where you can bring your case if you believe that you were wrongfully convicted.

It's run by prosecutors, some of them investigating their own colleagues.

You know, some of my clients and former clients are some of my favorite people.

The humanity that they exude and the resilience and their hope and their forgiveness.

Getting people out one at a time is exhausting.

We need to see why this is happening.

And fix it.

Next time we'll meet forensic science students working with the Los Angeles Innocence Project for KCET.

I'm Bonnie Boswell.

Bonnie Boswell Reports.

Is brought to you by the California Wellness Foundation.