So many people go into that environment gasping for air, drowning - that is exactly what it is like: nobody is going to pull you up except yourself

Paul Hill

The four had their convictions overturned in 1989 when it emerged that Surrey police had invented evidence against them, and lied under oath at their trial.

It was a revelation that put the entire justice system in the dock.

Dressed in a black Armani suit, Hill flashes a smile that reveals his $30,000 crowns.

He is sitting in a restaurant in a fashionable part of Washington, running his fingers through his trademark long hair.

Paul Hill: Long journey

The 1970s hair style is one of the few parts of his former life he has retained.

He is instantly recognisable from the hundreds of photographs of him which have appeared in the media over the years.

But these days his picture is more likely to be seen in society magazines.

He looks confident, healthy and expensive. It is hard to believe this was the same gaunt figure who walked out of the Northern Ireland Appeal Court in 1989 - the victim of one of the most notorious miscarriages of justice in modern times.

Every so often his American accent reverts into broad Belfast mid-sentence, as he recalls his prison years.

"So many people go into that environment gasping for air, drowning. That is exactly what it is like. Nobody is going to pull you up except yourself. It is literally like drowning."

BBC NI reporter Kevin Magee told Hill's story

In his mind, accepting the prison regime meant acknowledging guilt. He refused to conform, and was rewarded with a total of five years in solitary confinement.

"Imagine what it is like to spend 23 hours a day in a cell. You are basically encased in a concrete tomb.

"I was driven crazy by cockroaches. I had this Holy Jihad against cockroaches.

"In my better moments I would say: Is this what your life is reduced to? Is this how small your day is that you are down to searching a cell like a man on the verge of going crazy?"

Political elite

Since his prison days, life for Hill has taken a twist no Hollywood scriptwriter could have imagined. Today, he is dining at the top table with America's political elite.

He has met the President of the United States so many times he has stopped counting.

"He is always very focused on the north (of Ireland). He always gives you a little bit of time, and listens to what you're saying. And I know it has feedback. He's committed to Northern Ireland, and Northern Ireland is going to be part of his legacy."

Hill's marriage to Courtney Kennedy, the daughter of the assassinated American Attorney General Bobby Kennedy, and niece of JFK, has opened doors in Washington's corridors of power he could never have imagined.

Our histories had some kind of similarities in that we both had sufferance in loss

Courtney Kennedy Hill

Of all the changing fortunes in his life, it is his marriage into the most influential of all Irish-American families which has aroused the greatest interest.

"A lot of people think it's very unnatural. Here I am from west Belfast and I am married to Robert Kennedy's daughter. I don't feel any of that at all. I really don't.

"Partly because I am not phased by people, and they are just a normal family, but people tend to overlook that aspect of it because of tragedy."

The tragedy in his wife Courtney's life was the death of her uncle John F Kennedy, and father Bobby, both shot down by assassins.

She also lost two of her brothers - David, 29, from a drugs overdose and Michael, 39, in a skiing accident.

Courtney Kennedy Hill is the most private of Robert's surviving nine children, and normally refuses to give media interviews, but she agreed to speak exclusively to the BBC.

"It is an odd match truthfully, but one that came together, so it is a little bit different and it took us a little bit of time getting used to each other's kinds of lives and stuff. It was interesting to say the least," she said.

"I think there was some empathy and understanding that we had with each other that other people would not have. Our histories had some kind of similarities in that we both had sufferance in loss."

Spotlight producer Tony Curry

After several meetings with Spotlight producer Tony Curry, Hill agreed to take part in a frank documentary charting his life from west Belfast to Washington, via Wormwood Scrubs.

"I watched the Guildford story unfold, and was always very curious to find out how Paul Hill adjusted to life on the outside. It is a remarkable story when you consider everything that has happened to him," said Mr Curry.

During the making of the Spotlight programme, Hill stood inside his mother's house in New Barnsley, west Belfast, for the first time since his release from prison in 1989.

Paul Hill's mother Lily

It was the first time he had seen his mother, Lily, since he had a murder conviction against him overturned by the Court of Appeal in Belfast in 1994.

It was then that an outstanding conviction against Hill for the 1974 murder in Belfast of former soldier Brian Shaw was quashed.

It was found to be "unsafe and unsatisfactory".

Like Hill's Guildford and Woolwich convictions, it too was struck off, and he finally emerged from the court an innocent man.

As he sits in the Washington restaurant, the names of his new Hollywood friends roll off his tongue. He is a good friend of Tommy Lee Jones. Arnold Schwarzenegger is married to one of his wife's sisters.

Suddenly, he will change the subject and inquire about life back in Belfast.

"Is the herring man still selling fish door-to-door? Can you still get the eighth edition of the Telegraph? Do they still have decent pasties?"

It has been a long journey.

The two part Paul Hill story is being shown in Spotlight on BBC Northern Ireland on 6 and 13 June.