POLICE may already have the crucial piece of information that will lead to the arrest of the man who murdered a banker on his doorstep 10 years ago.

The identity of the man who shot Alistair Wilson, a 30-year-old married father of two children from Nairn, is still unknown, as is the motive for the murder.

However, police say they are still "entirely confident" the shooter will be caught and the case will remain open until he is.

As they prepare for the 10th anniversary of the murder, Mr Wilson's family yesterday made an appeal for anyone with any information to contact police.

Police also said they are eight weeks into a "complete deconstruction" of the investigation. This will re-examine every piece of information collected since the evening of November 28, 2004.

That was the Sunday night when a man described as being about 5ft 4in to 5ft 8in, of stocky build and wearing a baseball cap and dark blouson jacket, knocked on the door of the Wilson home in Crescent Road.

Mr Wilson's wife, Veronica, opened the door and the caller asked for Alistair Wilson by name. Mr Wilson came to the door, spoke to the man and at one point came back into the house with a blue or green A4 envelope.

He spoke to his wife, who was preparing their sons, four-year-old Andrew and two-year-old Graham, for bed. When Mr Wilson returned to the door, he was shot. The envelope was never recovered.

The biggest breakthrough in the police investigation was the discovery of the murder weapon - an East German Schmeisser handgun found by a council worker in a drain 10 days after the banker's shooting. The ammunition was .25 calibre and made between 1983 and 1993, in what is now the Czech Republic.

But it had never been licensed, and it did not lead detectives where they had hoped.

Detective Chief Superintendent Gary Flannigan, of the Specialist Crime Division Major Investigation Team yesterday said this was the first such "strategic review" of the investigation.

"Our determination on behalf of the family and the community will continue, however long it takes," he said. "We have every reason to think there will be an answer.

"History tells us that in these long-running investigations, the answer often lies within - some small piece of information, the significance of which was not seen originally.

"We want to see if somebody was telling us something we did not appreciate at the time. We have every reason to believe we will be optimistic."

He said that in the last 10 years science had moved on consider­ably. For example, there could still be progress on a DNA structure from a cigarette end found on the doorstep that had still to be identified, despite more than 1,000 samples being taken.

Since the start of the inquiry in 2004, the police have taken more than 4,100 statements; 2,700 productions held; and 11,000 actions raised as a result of investigations.

Mr Wilson's widow still lives in the same house with her sons. She, along with her husband's parents Alan and Joan and his sister Jillian, issued a joint statement that said: "The past 10 years, since Alistair's murder, have been extremely tough for our family. It has been 10 years during which his young sons started primary school, and then secondary school, without a father in their lives. It has been 10 years that his widow, Veronica, has been a single mother and the extended family left without the person we loved and cherished.

"It is difficult to achieve closure of our grief until we know why Alistair was killed on November 28, 2004 and who shot him. Despite years of searching for answers, the question which always remains is: Why?"

The family believes someone, somewhere knows the identity of Mr Wilson's killer.

"He has killed once; he may kill again and cause another family the heartbreak we have endured," they said.

There is a £5000 reward for information passed to the Crime­stoppers number (0800 555111) that leads to the arrest and conviction of the person responsible for the murder.