We begin today's

We begin today's story in a car, parked up on a bustling strip in Harlem.

From inside, two eyes trace a once-familiar landscape.

It's been 25 years since Edwin Eddie Ellis has walked these streets.

As he steps onto the sidewalk, the sounds of hip-hop and local children playing fills the air,

a stark contrast to the prison yard he's just left behind. He wonders how many of those children would also go on to spend decades locked in behind a barred

door.

This is not the first time he's considered the question.

Because for the past few years, Eddie has been conducting an investigation in prison,

unlike any that had been done before.

And it was time to take his findings to the public.

I'm Hannah Fry, a mathematician who studies patterns in human behaviour.

And from BBC Radio 4, this is uncharted. Tales of data and discovery.

A few years later, a researcher in Brooklyn named Eric Codora is working for the

Centre for Alternative Sentencing and Employment. Their aim was to find ways to deal with crime

that didn't just send people to state prison. And I was asked by the director of the agency to do what has been known in the United States

as skunk works, which is research into things we're not sure what we're trying to get at.

I just started reading.

Settling down with a cigarette, Eric is skipping through news reports trying to find something useful.

An interview from the New York Times catches his eye.

It was from 1992 and detailed the recent release of an activist named...

His name was Eddie Ellis.

...