What if he's not the killer next door?

Did a neighbour jailed for a police station murder really do it?

When it's still dark at 5am and the doorbell goes - that's when you can be pretty sure that you've got something to worry about. Either that, or someone is making a serious mistake.

There were two of them. They said they were detectives from Hammersmith police station. And they were apologetic, obviously on edge. In their way, which was a plain-clothes-detective, controlled kind of a way, they were highly agitated. "I can see you're probably not very impressed by the early morning call," said one. The other one said: "It's just that your next-door neighbour Mr Kennedy seems to have caused a bit of trouble last night and we need to, you know ..."

My neighbour, Mr Kennedy. Up here in London N16 we pride ourselves on actually knowing our neighbours, on not being inner-city strangers to those we live alongside. But perhaps the pride was misplaced because, when it came to it, I didn't know anything about Malcolm Kennedy. It was only later that I came to know quite a lot about this slight, diffident, middle-aged man whom I must have walked past and perhaps said "hello" to often.

Later that day Malcolm Kennedy was charged with the murder of a 56-year- old man, Patrick Quinn, a labourer. Nine months later he was convicted at the Old Bailey and received a life sentence.

Kennedy's flat lay empty for many months. It was repossessed, acquired a "for sale" sign and a broken window. But by then there was more than a suspicion that there was something very odd about his conviction.

To begin with, he made a strange sort of murderer. Described by everyone who knew him personally as shy and withdrawn, Malcolm Kennedy had no history of any sort of violence. But he had money worries and he was drinking. It was because he was drunk that he was arrested on the night before Christmas Eve in 1990. It was then he was taken to Hammersmith police station, and put in a cell with Patrick Quinn, who was also drunk.

What followed that night is uncertain. What is certain is that by the early hours of Christmas Eve, Patrick Quinn was dead. Quinn's heart and larynx were crushed. His ribs showed 33 fractures. One eye had been knocked from its socket. It was, as the prosecution at Kennedy's trial put it, "strange that anyone at all should have carried out such an appalling attack". But that was not all that was strange.

It has always been Kennedy's contention that some time during the night he was woken from a stupor by shouts, to find a man in a white shirt and dark trousers beating Quinn. When he tried to intervene, he was knocked unconscious himself. And when he finally came round, he says, Patrick Quinn was dead.

The police give an account that contradicts this entirely. The cell was opened a little before 2am on Christmas Eve, and Quinn was found lying in a pool of blood. The body was covered with prints from Kennedy's shoes. Kennedy himself was thoroughly smeared with Quinn's blood and his scarf and heavy chronograph watch were lying, bloodstained, on or near the body. No one heard anything.

In other words, no credible witnesses to this murder have come forward. Kennedy's recollection is, by his own account, virtually worthless. There are just two explanations, and a mass of forensic and documentary evidence. Judging between the two means judging which is the more coherent, the more consistent, and the more plausible.

Plausibility has always been on the side of the police: every day of the week obstreperous drunks pass through their hands without suffering anything worse than a hangover. But after three trials, two sentences and one appeal, few would say that in this case the police have either consistency or coherence on their side. Even at the time of the first trial in September 1991 it was apparent that something had happened to the documentary evidence that should have supported the prosecution case. A subsequent investigation by the Police Complaints Authority found that "a majority" of the relevant pocket books and other police documents could not be found. Was that because those documents would have revealed a very different sequence of events from that outlined by the prosecution? Unanimously the jury rejected that possibility.

However, evidence in Kennedy's favour continued to emerge. By the following year Granada TV's World In Action had found two witnesses who contradicted the police account of the timing of that night's events.

The appeal that followed was damaging to the prosecution. In giving evidence police officers flatly contradicted each other, although the prosecution continued to argue that these inconsistencies were due to "the passage of time". The prosecution also presented new evidence - in particular a lost police pocket book that a Hammersmith police officer claimed to have found accidentally hidden behind a current pocket book. In a classic piece of court theatre, defence counsel Michael Mansfield QC asked him to demonstrate how it was hidden: it wouldn't fit. Kennedy's murder conviction was quashed, and a retrial ordered.

By this point the defence had a powerful case: the timing of events in the police version was in serious doubt, and timing was crucial to the question of whether the Hammersmith police could have had enough time to fabricate a cover-up. There were also doubts about the quality of the forensic evidence against Kennedy, and witnesses who described an atmosphere of near-panic in the police station long before the official discovery of the murder. And by this point Quinn's family had also come to doubt Malcolm Kennedy's guilt.

But the defence did not get the opportunity to cross-examine the police officers who had given contradictory evidence at the appeal. The trial was halted midway when the prosecution announced the discovery of another "lost" document. Kennedy now faced the prospect of a third murder trial. Around this time he wrote to me, enclosing a mass of documentation about his case.

Malcolm Kennedy is - as his solicitor Michael Schwarz puts it - "not the most fluent of individuals". He is not the sort of person who makes a good miscarriage-of-justice hero. But as Schwarz says, "he is very determined, very single-minded, very focused on just one thing, which is to clear his name". And he believes fervently that somewhere the evidence exists that will prove he did not kill Patrick Quinn.

The third trial, however, was to be a disappointment. The examination of police evidence which had been so effective at the appeal was not repeated. The court accepted that written statements from the police officers involved could be read out, partly because PC Giles, the officer who arrested Quinn, was said to have become too mentally unwell to face giving evidence a fourth time. And although the charge was murder, the judge offered the jury the option of returning a verdict of manslaughter - which they did. Kennedy was sentenced to nine years.

In the appeal against this sentence, due to be heard on Tuesday, the defence will argue mainly on legal grounds, attacking the conduct of the last trial when witnesses were not cross-examined. It is unlikely that the underlying issue - the consistency of police evidence - will be re- examined. But that remains the central issue. Michael Schwarz said: "When there are irregularities in police records one can often put it down to slapdash work. But there comes a point when there are so many irregularities that it starts to point to something else, perhaps a cover-up. That is the point we are at in Malcolm Kennedy's case."

It is nearly seven years since the murder of Patrick Quinn. Kennedy's flat has changed hands several times, thanks to the reviving property market. It's tidier and smarter now. The days of repossessions and broken windows seem to have gone. Is it also time for Malcolm Kennedy, released on parole earlier this month after serving four and a half years, to let things lie, to move on?

"He cannot do that," says Michael Schwarz. "If that's difficult to understand, just try to imagine this: what if Malcolm is right? What if he didn't kill Quinn? What does that imply?"

To me, the point is clear. It means that it could just as easily have been Malcolm who was woken at 5am by those detectives that morning six years ago. They would have asked him about his neighbour, about me, the murderer.

Of course he wouldn't have been able to tell them anything. He didn't know me.

Malcolm Kennedy's appeal begins on Tuesday.