The investigation into the assassination of the man who helped put road rage killer Kenneth Noye behind bars is still open, more than 20 years later.

Alan Decabral, from Pluckley, was a key witness during Noye’s trial in April 2000 for the murder of Stephen Cameron, 21.

But he was shot dead just months later on Thursday, October 5, 2000, within sight of hundreds of lunchtime shoppers in Ashford.

Father of three Mr Decabral was sitting in the passenger seat of a black Peugeot 205 waiting for his son at the Warren retail park in Simone Weil Avenue, when a man pointed a gun through the open window and pulled the trigger.

Witnesses at the time described how they heard Mr Decabral beg for his life to be spared.

A young man wearing a woolly hat was seen fleeing from the scene, which led to a massive manhunt at the time by Kent Police.

But the murder remains a mystery to this day, as no one has ever been convicted.

It was revealed after the killing that Mr Decabral, 40, gave evidence against Noye at his 12 day trial.

Noye killed Mr Cameron, 21, in a road rage dispute on the M25 near Swanley in 1996.

He stabbed the young electrician in front of his girlfriend before escaping the scene and going on the run in Spain.

But he was extradited in 1999 and went on trial the following year.

Mr Decabral told the Old Bailey he had seen two men fighting on a slip road of the motorway and saw Noye “lunging forward” with a knife and stabbing Mr Cameron.

But he said he feared for his life after speaking out.

After the trial, Mr Decabral told The Telegraph: “Giving evidence against Kenny Noye had a devastating effect on my life.

“I split from my wife because of the stress and I had to shut down my motorbike business because I have received death threats.

“I am constantly looking over my shoulder because I could be a target.”

He also described a meeting with a man who told him: “I was told that I could either shut up or I would be shut up.”

After the trial, Noye, now 71, claimed Mr Decabral was an unreliable witness who created an “edifice of lies” about Noye as a bargaining tool with police.

And even his estranged wife Anne Marie said she did not believe her husband’s story because he regularly exaggerated.

“I am constantly looking over my shoulder because I could be a target...” - Alan Decabral speaking shortly before he was shot dead

He was also revealed by police as a career criminal with links to drugs, firearms trading and smuggling drink and tobacco.

At an appeal hearing in 2001 Noye’s barrister Michael Mansfield QC said: “He was alive to the fact the police had an interest in him.

“As a result of his criminality and vulnerability he had a motive to lie in 1996 when giving his statement - he had a bargaining tool.

“In his 999 call he claimed he had seen a gun - there was no gun.”

After Mr Decabral’s murder, Kenneth Noye was questioned by police but they concluded that it had no proven connection with him.

Other theories suggested Mr Decabral was a former Hell’s Angel caught up in a war between biker gangs, fighting for control of a lucrative drug trade and this was the motive for his killing.

Again, this was not proven.

A Kent Police spokesman said: “Alan Decabral, aged 40, of Pluckley was murdered in October 2000.

“To date, there have been no charges in relation to his death.

“The file on this case remains open and, as with all unsolved major crimes, Kent Police regularly review cases.”

Anyone with information about Mr Decabral’s murder should ring Kent Police on 01622 690690, or call Kent Crimestoppers anonymously on 0800 555 111.