It was the sort of thing that happens in every city every weekend. But this late-night row at a cab rank ended in tragedy when words exploded into violence.

The man on the end of a punch, Jay Abatan, hit his head on the ground and subsequently died.

Mr Abatan, a father of two and described by his partner Tanya Haynes as the "best dad in the world", never emerged from his coma.

His death triggered the second largest inquiry Sussex Police has undertaken, next to the Sarah Payne investigation.

After more than four years of police inquiries costing £2 million, no one has been brought to justice and ten days ago the case claimed a second life.

Graham Curtis, once charged with Mr Abatan's manslaughter, was found hanged at his home in Port Hall Road, Brighton.

He had suffered with depression, partly due to him splitting with his girlfriend and, according a friend, partly because police were still bothering him.

He had been in the frame soon after Mr Abatan's death in 1999. Mr Curtis, 40, and a second man were charged with the manslaughter of Mr Abatan, 42, but the cases were dropped after Brighton magistrates ruled there was insufficient evidence.

The following year, both men were cleared of assaulting Mr Abatan's brother Michael.

A scuffle had started after a dispute with another group over who had ordered a cab to take them from the the Ocean Rooms night club in Morley Street, Brighton.

Jay Abatan, of Meads, Eastbourne, was attacked and sent crashing to the pavement. He was motionless as the taxi drove away and died in hospital from head injuries.

Mr Curtis' friend Mark Owen said being the focus of a police inquiry for four years got his friend down, although he did not believe it was the sole reason for Mr Curtis' depression.

Mr Curtis had recently split with his girlfriend.

He said: "They had a big house and Graham had spent a lot of time doing it up. He had lived there on his own for a couple of months before he died. He had recently been trying to sell it."

Mr Owen and Mr Curtis worked together for two years as editorial systems analysts at News International, publishers of The Sun and The Times, in Wapping, east London.

Mr Owen said: "He and I were partners and I got to know him as much as people get to know one another.

"He was complicated but a very talented man. He may look a bit like a thug in his picture, with his shaven head, but nothing could be further from the truth.

"He was a really nice bloke, very clever, with a good sense of humour and very genuine. All of us who knew him were devastated by news of his death."

Mr Owen said one bout of depression suffered by Mr Curtis was triggered when news broke of a possible private prosecution by the Abatan family.

Any time Mr Curtis made a new friend, they would receive a visit from the police, asking questions about him.

Mr Owen said: "They knocked on my wife's door once and said they were there on a murder inquiry.

"When Graham bought a computer they took it away to check what was on it. And they checked his mobile phone calls. It did get to him."

Mr Curtis was affected by media reports on the Justice for Jay campaign which spoke of a "vicious" attack on Mr Abatan.

Mr Owen said: "It should never have happened but, as I understand it, it was a row over a taxi which resulted in one punch in the face. They were all in the wrong place at the wrong time.

"Every now and then Graham would get really down and I'd try to cheer him up.

"He had plenty to live for. He was very talented, a great snow-boarder, a diver and he taught trainees at News International.

"Graham was a great Southampton FC supporter, that's his home city, and with me being an Arsenal fan we would rib each other, especially over the FA Cup final.

"Graham had everything to live for. He'd even bought next year's season ticket for Southampton.

"He had been portrayed wrongly ever since the incident. They said it was a racist attack, meaning Graham must have been a racist, but that's just not true. Graham worked with lots of black people and there's no way he was racist.

"He felt sorry for Mr Abatan and his family and completely regretted what happened."

David Lepper, MP for Brighton Pavilion, wants to know why police pursued Graham Curtis for so long.

He said: "Here is a man who was twice cleared in court.

"I want to know why this case proceeded as far as it did when neither of the charges against him could convince the courts of any guilt on his part."

Mr Lepper said the launch of a new Criminal Justice Board, to ensure the right cases get to court, arrived too late for Mr Curtis.

Jane Lloyd, a solicitor who represented Mr Curtis up to the point of his acquittal on the affray charge, said her client had felt he was being pestered by police.

She said Mr Curtis was found innocent of any crime and was of good character. She added: "I was so upset when I heard of his death."

Mike Whippy, Mr Curtis' legal representative after the court action, recalled one occasion last year when his client was arrested and taken to Crawley police station. He spoke with Mr Curtis on the telephone.

Mr Whippy said: "He asked me when this was all going to stop. "A long list of Mr Curtis' relations were questioned by police."

Mr Whippy said Sussex Police conducted themselves professionally and properly but he felt sorry for them because they were under pressure.

Criticism over the death of Stephen Lawrence and the ensuing Macpherson Report led to pressure on police over the way they dealt with racially motivated crime.

There was no evidence found of racism in the inquiry into Mr Abatan's death but his brother Michael has always maintained there was.

That was all that was needed for Sussex Police to treat the death as a racist murder.

Their first inquiry into Mr Abatan's death was heavily criticised after an inquiry by Essex Police. The review listed 57 conclusions, mostly critical, and 18 recommendations.

It said no lateral thought was given in the original investigation as to whether Mr Abatan's murder was racially motivated.

The report said Sussex failed to pick up Macpherson Report recommendations on proper liaison with the victim's family and said it was surprised lessons listed in the report were not taken on board by officers investigating Mr Abatan's murder.

Sussex Police later publicly apologised to the Abatan family but Graham Alexander, of the Sussex Police Federation, said he was not happy.

While the report produced "good and sensible" changes, he felt there was danger of forces over-reacting and of interpreting them in a "fanatical" way.

A Police Complaints Authority inquiry is continuing to investigate whether officers involved in the first inquiry should be disciplined.

Mr Alexander said the length of time it was taking had wreaked "pain and frustration" on officers' lives.

He said officers sometimes had to make instant decisions and those working the night of the attack on Mr Abatan "tried their level best" to get things right.

He was worried systems of accountability by "armchair critics" were undermining hard-working police and the service itself.

Michael Abatan, Jay's partner Tanya Haynes and West Worthing MP Peter Bottomley launched a Justice for Jay campaign to highlight the case and press for more information from witnesses.

The family and Sussex Police are offering a £175,000 reward for information leading to the arrest and conviction of those responsible for Mr Abatan's death.

Anyone with information should call Sussex Police on 0845 6070999.