I lived to tell the tale, but what about Sam?: Jan Ariens had been writing to a prisoner on death row in Mississippi for five years. He travelled there to be a character witness in a retrial for his friend

Wednesday 14 October: Jackson, Mississippi. I am here to testify at a death penalty trial. Sam Johnson, black, 50, is accused of killing a white policeman on New Year's Eve in 1981. He has been on death row for 11 years; we have been corresponding for the past five. Sam has been given a resentencing trial and I have been called as a character witness. In 1988, the US Supreme Court overturned the grounds on which Sam was originally given the death sentence. Under American law, while Sam remains guilty, a new trial has to be held to determine an appropriate sentence. In effect, this means a rehearing so that the new jury can assess the facts.

I am met by Clive Stafford Smith, a 31-year-old British lawyer who works for the Southern Center for Human Rights in Atlanta, and is defending Sam. Clive warns me to keep my testimony simple. Any attempt to portray Sam as someone out of the ordinary could be counter-productive.

At a motel in Vicksburg I meet some of Sam's 20 relatives and friends who have travelled the 1,500 miles from Rochester, New York, by Greyhound bus to testify and support him. None of them, including his wife, Shirleen, has seen him for the past 11 years. They could not afford the trip. Now it has been paid for by Clive's office.

Thursday 15 October: In the morning I go briefly to the courtroom to attend the jury selection. As we are waiting, an extremely well-

dressed black man walks in. Momentarily I fail to recognise him; the last time I saw him, in 1988, he was in a red prison jump-suit. It is Sam. Later I meet him briefly during a recess: we shake hands and say, 'We'll get there, bro.'

Friday 16 October: A panel of 80 jurors is left. On the surface, the screening process is an impressive display of American justice, as great care is taken to exclude potential jurors who might be biased on racial or other grounds. As a verdict in favour of the death penalty has to be unanimous, those opposed to capital punishment are excluded. While this is inescapable, it means that the jury is not fully representative of all opinions. Meanwhile, after 11 years apart from Sam, Shirleen is denied a 'contact' visit in the same room.

Saturday 17 October: Sam calls me collect at the motel. He is, as ever, optimistic and full of warmth and humour, pulling my leg that one of his nieces has fallen for me.

There are 16 blacks, and - according to Clive's team - some liberal-minded whites in the remaining pool of 38 jurors.

Sunday 18 October: We visit Sam in normal visiting hours - more than 20 of us in the narrow corridor. He is behind glass and we have to speak through a tiny gauze strip. If you have eye contact, you can't make yourself heard without shouting, and if you bend down to speak, you can't see one another.

Far from the long faces and heaviness one might expect on such an occasion, there is lots of banter and laughter. Sam booms through the gauze, 'Man, I want to get out of Mississippi so bad. If they cut off my arms and cut off my legs, I'll just roll out.'

Monday 19 October: The 38 remaining jurors assemble in court. I am surprised at the emotion I feel as the names are called out of those who are to serve. Not only do they have Sam's fate in their hands, but they are being asked to weigh a person's life. No one, I feel with conviction, should ever be placed in such a position. Four are black, which is promising.

Sam makes a nervous but dignified statement that he will not himself be testifying.

Tuesday 20 October: The defence has clearly made an impact. At the end of the day, Jackson TV runs a news item entitled 'Is the wrong man on Death Row?'

The 1981 killing occurred after Patrolman Billy Langham stopped a car with four black passengers. Prosecution witnesses admit that the fingerprints of another of the four, Anthony Fields, were found near the rear door of the car, where the initial struggle took place when the officer was stabbed, and that the assailant was stocky - which Sam is not.

The deputy sheriff is angry that Sam's relatives are being demonstrative in court. 'If ah ketch y'all smilin' or wavin' at the prisoner any more, ah'll have y'all expelled from court.'

Wednesday 21 October: Clive decides to reduce the number of witnesses. The 'residual doubt' angle has gone well, and the jurors can return the death penalty only if they are convinced Sam is guilty beyond reasonable doubt. It is not worth the risk of exposing witnesses to potentially damaging cross-examination. I, too, will not be required to testify. I am disappointed, but accept that Clive is acting in Sam's best interests.

The morning session is devastating. Fields, the main prosecution witness, takes the stand. In 1982 he pleaded guilty as an accomplice after the fact and turned state's evidence. The prosecution's case is based on Fields's version of events - while Sam maintains it was Fields who stabbed Langham.

Clive's cross-examination is a tour de force. On point after point, Fields is forced to admit that his previous testimony was inconsistent. Particularly absurd is his story as to how the murder weapon got into Sam's hands. We are asked to believe that, having frisked Sam and later discovering a butcher's knife in the car, Langham, an experienced highway patrolman, then lined the four men up against his patrol car placing the knife on the roof. ('Don't touch, boys.')

In the afternoon I am greatly moved by the sometimes halting testimony of Sam's relatives, who stress he has always been a man of non-violence. A nephew who is a policeman testifies on video how Sam helped to save the police chief in Rochester from harm during a race riot.

Thursday 22 October: A forensic pathologist testifies that the cuts on Sam's right hand - said by the prosecution to have been sustained in the stabbing - must have been made when trying to drag off the assailant. A former Roman Catholic staff chaplain to death row inmates and one of Sam's former prison guards both testify in Sam's favour.

Friday 23 October: The closing argument is presented. 'Fields told more lies than anyone in the space of two hours,' Clive tells the jury. Trying to be as objective as I can, I find it very difficult to believe that any fair-minded person could still regard Sam's guilt as 'beyond reasonable doubt'. Even if they do, they must then consider the crime to be sufficiently serious to warrant the death penalty after allowing for the eight mitigating factors in the judge's instructions.

The jury retires at 2pm. All afternoon the family and other supporters wait in a nearby office. Time creeps by. At 7pm the judge instructs the jury to retire for the night. I talk briefly with some of the victim's family, expressing Sam's sorrow at what happened, but they are in no mood for a reconciliation.

That evening we let our hair down at the motel, dancing and singing; light relief is essential, and we cannot now believe that the verdict will go against Sam.

Saturday 24 October: At 10am we receive the call to go the courthouse. As the jurors take their places the faces of the six middle- aged white women are suffused with anger; the jury is unable to agree. The judge then hands down a life sentence (with automatic possibility of parole).

Many of those on Sam's side weep and rejoice at the verdict. There is happiness that Sam will not return to death row, but I am sick at heart at the attitudes of the prosecution and white members of the jury. (We later learn that the jury split seven-five, with seven of the eight whites wanting the death penalty.) And will Sam ever make parole?

After the trial, the victim's widow states on television that when Sam is released, she hopes he will not kill those who voted for life. To Clive she says, 'I hope he gets out and kills you because you are the scum of the earth.' Clive can only express his deep regret at all that she has been through.

After losing her husband in a wanton murder, and having to endure two trials, her bitterness may be understandable. But it is also fostered by a system in which justice is equated with vengeance. Meanwhile, Sam has lost 11 years of his life waiting for a punishment now deemed inappropriate - and his wife and family have suffered, too. Nevertheless, at the end of it, Sam can still say: 'This experience and these people have taken me so low that I have to reach up to touch the bottom. But I still believe in mankind.'

The author is the chairman and founder of Lifelines, whose members write to prisoners on death row in America. His book, 'Welcome to Hell', a collection of writing by prisoners, is published by Ian Faulkner Publishing, pounds 9.95.