The family of Jean Charles de Menezes is taking his case to Europe's Court of Human Rights a decade after his death.
They want to challenge the decision not to prosecute any police officers over the shooting of the innocent Brazilian electrician at Stockwell tube in 2005.
Lawyers for his family believe the failure to prosecute individual officers breached his rights under Article 2 of the convention.
The court must now determine whether the state failed in its obligation to protect his right to life.
His cousin Vivian Figueiredo told ITV News if no-one is held to account, the same could happen again.
ITV News UK Editor Rohit Kachroo reports: