Law Lords are reviewing a controversial court finding that criticised police for failing to protect a man who was gunned down by a bitter employee.
Wembley optician Giles Van Colle, 25, was shot three times at close range, outside his shop in Mill Hill, in 2000.
He was due to give evidence against former worker Daniel Brougham, who he had sacked for stealing, but was brutally murdered before the trial started.
Brougham was found guilty of the attack at the Old Bailey in 2002 but Mr Van Colle's family sued Hertfordshire Police for not offering their son sufficient protection.
In a landmark ruling in March 2006, the High Court found in favour of the family and said there had been a violation of his human rights laws.
They were awarded £50,000 in damages but police chiefs appealed against the decision.
The four-day hearing was held at the Houses of Parliament last week and altxxxgh the judges threw out the police appeal, the payout was reduced to £25,000.
The Van Colle family have now lodged a cross appeal against the decision to halve the damages.
The optician's father, Irwin Van Colle, said: "The police were appealing against the previous judgement that found them to have breached my son's human rights. The appeal was dismissed but our damages were halved and we have now cross appealed against this."
At the hearing, the law lords reserved their judgment and are expected to take around two months to make a decision.
Mr Van Colle added: "I can not say when the judgement is going to be made but I will make a full comment on the case once the lords do so.
"It is not very pleasant taking significant litigation for the reasons we had to but it is now in the hands of five of the most senior judges in the land and it is up to them.
"Significant issues have been raised in the case and I am sure they will want to deliberate on this for as long as they need."
Mr Van Colle, who is a Conservative councillor in Brent, has not received any money from the police and will have to wait to see if his cross appeal is accepted before he can do so.