The family of Jean Charles de Menezes will challenge the decision not to bring charges over his death at the European Court of Human Rights (ECHR) today.
Relatives of the Brazilian will take their case to the Strasbourg court's Grand Chamber almost 10 years after he was mistaken for a suicide bomber and shot dead by police marksmen on a London Tube train.
Lawyers for the family argue that the assessment used by prosecutors in deciding that no individual should be charged over the 2005 shooting is incompatible with Article 2 of the European Convention on Human Rights, which covers the right to life.
They claim the evidential test applied by the Crown Prosecution Service - that there should be sufficient evidence for a "realistic prospect" of conviction - is too high a threshold.
It means that, in effect, the decision not to bring a prosecution was based on a conclusion that there was less than a 50% chance of conviction, they say.
The case has been lodged by Patricia da Silva, a cousin of Mr de Menezes.
She said: "For 10 years our family has been campaigning for justice for Jean because we believe that police officers should have been held to account for his killing. Jean's death is a pain that never goes away for us.
"Nothing can bring him back but we hope that this legal challenge will change the law so that no other family has to face what we did."
Mr de Menezes, 27, was shot dead by Metropolitan Police firearms officers at Stockwell Underground station in south London on July 22 2005.
The following year the CPS announced that no individual should be charged.
In 2007 the Met was fined £175,000 after being convicted of breaching health and safety laws.
An inquest jury later rejected the police account of the shooting and returned an open verdict. The coroner had already ruled out a verdict of unlawful killing.
In 2009, the family of the electrician agreed an undisclosed settlement with Scotland Yard.
Today's hearing comes more than seven years after the original application was lodged at the ECHR. The claim is also challenging the definition of self-defence.
Harriet Wistrich, a solicitor representing the family, said: "The officers who shot Jean Charles have a defence if they had an honest belief that they were under imminent threat, even if they were mistaken and their mistake was wholly unreasonable."
Judgment is expected to be reserved. The CPS declined to comment ahead of the hearing.