The son of a banker who was shot on his doorstep has said he still has nightmares about his father’s murder.

Andrew Wilson, then aged four, saw his father Alistair lying in a pool of blood after he was shot at their home in Nairn, in the Highlands, on November 28, 2004.

He told on Tuesday how he has blanked out many of his childhood memories as a way of dealing with what happened.

In September, Scotland’s top law officer Lord Advocate Dorothy Bain KC ordered a complete reinvestigation of the case with a new team of police officers and prosecutors.

Scotland’s First Minister John Swinney said it is important police remain focused on bringing the perpetrator to justice.

Police Scotland Chief Constable Jo Farrell has said officers have a “resolute determination” to solve the murder, but the Wilson family have questioned whether she is fit to lead the force.

Mr Wilson said he is haunted by what happened on that day just over 20 years ago.

He told Sky News: “All I saw was my dad on the floor in a pool of his own blood. My mum over him. I still get the image of my dad himself in nightmares and stuff from time to time.

“I blanked out a lot of my childhood memories, that was my way of dealing with it, just kind of closing the door on that kind of part of my life.”

Alistair Wilson was shot at about 7pm on Sunday November 28 after a man called at the family’s home on Crescent Road, spoke to his wife Veronica, who had answered the door, and asked for her husband by name.

The 30-year-old went downstairs to speak to the man and was handed a blue envelope with the word “Paul” on it.

He went inside briefly and then returned to the door for a second time, where he was shot and died later that evening in hospital.

The gun, a Haenel Suhl pocket pistol from the 1930s, was recovered from a drain near his home 10 days after his murder.

After the reinvestigation was launched, the family said they have lost confidence in the police.

We are committed to this reinvestigation

Asked by Sky News whether Ms Farrell should resign over the issue, Andrew Wilson said: “There’s no other option. I felt that if she can’t get a grasp of what’s going on, then how can she lead?”

Ms Farrell said Police Scotland are committed to the investigation and urged anyone with information to contact them.

Speaking at a Scottish Police Authority Board meeting last Thursday on the 20th anniversary of the murder, she said: “I would repeat our appeal that anyone with information please contact us, on 101 or through the dedicated online portal which can be found on our website.

“A new investigation team is in place and detectives will examine all evidence gathered over the last 20 years, as well as investigate new opportunities for fresh lines of inquiry, such as advances in technology and forensic testing.

“We are committed to this reinvestigation and I would underline our support for Alistair’s family and our resolute determination to bring those involved in Alistair’s murder to justice.”

Asked outside the meeting whether she will resign, Ms Farrell told Sky News: “I won’t be resigning. I am committed to us getting answers and finding the people responsible for the murder.”

Mr Swinney said Ms Farrell has assured him police are focused on catching whoever murdered Mr Wilson.

He said: “I understand the depth of the concern of the Wilson family, and I cannot imagine what it has been like to experience the sense of loss that they have experienced in such awful circumstances for the last 20 years.

“I have every sympathy with the sense of injury and suffering that the Wilson family have, and what I’m assured by the Chief Constable is that her team are focused on trying to bring to justice the perpetrator of this murder.

“It’s important that that remains the focus of Police Scotland, and that they deploy the energy and the resources that the Chief Constable has made clear are being deployed to make sure that the perpetrator can be brought to justice.”

Police have launched a public portal where people can submit information about the murder which can be accessed at https://mipp.police.uk/operation/96HO020108N02-PO1.