The parents of a trial witness murdered days before giving evidence have been awarded £50,000 in damages.
Mr Van Colle had received several threats to drop the case
Optician Giles Van Colle, 25, was shot dead by former employee Daniel Brougham at his shop in Mill Hill, north London.
His parents brought the action against Hertfordshire Police claiming they had done "nothing" to protect their son.
Brougham had been facing theft charges, including from Mr Van Colle, and had repeatedly threatened the optician before he murdered him in 2000.
Brougham, 36, who was born in Iran as Ali Amelzadeh but used a variety of names, was jailed for life in March 2002.
Mr Van Colle's parents, Irwin and Corinne, said the police had failed in their duties under the Human Rights Act.
Their QC Monica Carss-Frisk said police "not only did nothing to protect Giles but did not even address the need to protect this crucial witness".
The police force had denied liability and said the "appalling" murder was impossible to predict.
Edward Faulks QC, representing the police, said: "It is not possible to conclude that any action by the officer would have altered the eventual tragic outcome."
Brougham worked at the optician's until 1999 but after he left he was arrested and charged with theft. He was released on bail.
After Mr Van Colle agreed to be a witness at the trial, his car was set alight and he received threatening calls from Brougham.
In October 2000, Brougham telephoned him saying: "I know where you live.
"I know where your businesses are and where your parents live. If you don't drop the charges you will be in danger."