Five Iraqis have been cleared of the murder of six British Royal Military Police officers in 2003.
Nick Harvey, the Armed Forces Minister, said an Iraqi judge had ruled five of seven suspects arrested earlier this year had no case to answer. Two remaining suspects are now expected to face trial.
The Army Red Caps were killed after a 400-strong Iraqi mob descended on a police station in Majar al-Kabir in June 2003.
Relatives of the victims have fought a long campaign for justice. In January 2008, Iraq's interior minister, Jawad al-Boulani, vowed to track down the killers after a letter from three of the families implored him to find the culprits.
A Ministry of Defence spokesman said yesterday the UK Government was committed to seeing the killers brought to justice.