As he walked past my car he nodded to me as if to say: 'That sorted him out'

Alan Decabral

"Anyone who saw him or indeed anyone with information about the incident is asked to call the incident room.

"We are appealing now for anyone at the retail centre and its car park between 12.30pm and 2pm today to contact us," she said.

Kent Police declined to say if they would be interviewing Kenneth Noye as part of their investigation of the killing.

Mr Decabral saw Noye stab 21-year-old Mr Cameron in a road rage incident on an M25 sliproad at Swanley, Kent, in May 1996.

At the trial at the Old Bailey, Mr Decabral, a Rolls-Royce driver, explained how he saw Noye hide a knife behind his back before lunging and stabbing Mr Cameron in the chest.

He told the court: "I saw a bright flash and I realised it was a knife because I could see the sun glinting off the blade."

Mr Decabral said Noye then closed the knife and walked past his car.

"As he walked past my car he nodded to me as if to say: 'That sorted him out, you've got yours mate', that sort of thing," he told the court.

Alan Decabral: Death threats

Mr Decabral then called 999 before attempting to follow Noye's Land Rover Discovery.

He later helped police build up an e-fit picture of Mr Cameron's attacker and gave them a detailed description of what he was wearing.

Police have confirmed that a man in his early 20s led away in handcuffs from Mr Decabral's home on Friday has been arrested.

It is understood he is not a member of the Decabral family and that he was arrested for an alleged theft.

The arrest was entirely unconnected to the murder investigation, they stressed.

He was taken out of the front door of a house in Pluckley, Kent, by three police officers and put into the back of a patrol car before being driven off shortly after 1000 BST.

'Told to shut up'

In July this year Mr Decabral told the Sunday Mirror that he had been threatened in an attempt to stop him giving evidence in court.

The father-of-three said he was ordered by "gangsters" to "shut up or we will shut you up" and became "terrified" after three bullets were pushed through his letter box with another warning.

Mr Decabral said he had to shut down his vintage motorbike shop in Acton, west London, because he could not cope with his life being threatened, and later separated from his wife.