'What do we have to do to get justice?'

The distraught parents of Stephen Lawrence, the A-level student murdered by a gang of racists, vowed to continue their fight for justice yesterday after their private prosecution of three white men collapsed.

Neville Lawrence, Stephen's father, said later: "I believe in fairness. I don't think what happened today is fair at all."

Neil Acourt, 20, Luke Knight, 18, and Gary Dobson, 20, walked free from the Old Bailey after the judge ruled a witness's evidence inadmissible.

Michael Mansfield QC, who had brought the private prosecution on behalf the family - only the fourth in 130 years - said the other material including covert surveillance videos and scientific evidence was not sufficient to put before a jury.

The video, shown at a committal hearing, revealed the defendants wielding knives, uttering extreme racial abuse and fantasising about killing, torturing and mutilating blacks. A police search found seven knives, including a Gurkha kukri, at one of their homes.

The collapse of the case will be seen as a vindication of the Crown Prosecution Service's earlier decision not to pursue the case for lack of evidence.

But Imran Khan, the family's solicitor, rejected that suggestion as too simplistic. He said the Lawrences had been let down by the "entire criminal justice system". He said the initial police investigation had been flawed, the CPS should not have abandoned the case - and the decision to rule out the witness evidence was both "surprising and unfortunate".

Stephen, who was studying to become an architect, was 18 when he was attacked as he waited with his friend Duwayne Brooks at a bus stop in Eltham, south London, in April 1993. Mr Mansfield had claimed the three were part of a gang of racists bent on the "desecration of those who were black by injury or possible death".

He told the jury: "There can be no question that whoever did this was someone who had a deep felt hatred of black people existing."

However, the case foundered when Mr Justice Curtis said the identification of Luke Knight and Neil Acourt by Mr Brooks, 21, was contradictory and contaminated.

The court was told how Mr Brooks had suffered from post traumatic stress after the attack. The judge refused to allow his evidence to be put before the jury ruling that it "would amount to an injustice" to do so.

The judge said: "However horrible the crime and objectionable the motive", it did not allow him to remove or alter the legal safeguards which protected anyone from a misidentification. "Putting one injustice on top of another does not cure the first injustice done to the Lawrence family," he said.

Mr Justice Curtis praised the Lawrences for their decision to drop the case "in the interests of justice and fairness". He granted the family their costs out of central funds.

Last night Mr Lawrence, unusually alone because his wife Doreen was too upset, said the family would continue to search for Stephen's killers. He added: "I would like to thank all the supporters from the last three years, black and white, old and young."

But Azim Hajee, a friend and campaigner, said most people would now be asking "what went wrong". "What is it that black people have to do, that ordinary folk have to do, to get justice?" he said.