Giles Van Colle was shot dead at the back of his shop

Giles Van Colle, 25, was shot dead outside his shop in Mill Hill Broadway, north-west London, in November 2000.

Killer Daniel Brougham had threatened the optician because he was due to testify against him in a theft trial.

Hertfordshire Police is being sued in the High Court, London, over claims it did not respond to death threats.

Giving evidence on Friday, David Ridley, the officer involved in the case, who is now working as a detective sergeant in the same Hertfordshire force, agreed he had not considered providing protection for Mr Van Colle.

"It is something I deeply regret," he told the judge.

Brougham was convicted of murder in 2002

He admitted he had never seen the guidelines on how witnesses should be protected although they were on a police internet site.

Mr Ridley admitted that, if he had followed the guidelines, he should have arrested Brougham.

The officer was found guilty by a disciplinary tribunal in June 2003 of failing to perform his duties diligently, failing to investigate thoroughly the intimidation of witnesses and failing to arrest Brougham.

He told the judge: "I have been shown to be wrong and I accept I made the wrong decision, the wrong judgment, at that time.

It is not possible to conclude that any action by the officer would have altered the eventual tragic outcome Edward Faulks QC, for Herts Police

"I accept he was in danger. Looking at it now and what happened, yes. But I did not think that at the time."

Earlier lawyers for the police admitted that the death of optician Mr Van Colle might have been avoided if the officer in charge of the theft inquiry had responded to the threats.

But Edward Faulks, QC told the court it would have been difficult to predict the "appalling and drastic" action taken by Brougham.

"It is not possible to conclude that any action by the officer would have altered the eventual tragic outcome," said the lawyer.

The victim's parents, Irwin Van Colle, a Tory councillor in Brent, north London, and his wife, Corinne, are claiming unlimited damages from Hertfordshire Police under the 1998 Human Rights Act.