Five Iraqis accused of murdering six Royal Military Police officers in 2003 have had their charges dropped, the Ministry of Defence has confirmed.
Only two men will now stand trial in Iraq, possibly later this year, after an Iraqi judge ruled that the five in question had no case to answer.
The military police officers - or Red Caps - were killed by a mob in the town of Majar al-Kabir in southern Iraq.
John Hyde, the father of Ben, who died aged 23, said he was disappointed.
He told the BBC: "The problem is it's going the wrong way.
"What we expected to happen was that the people that they had in custody would be prosecuted and further outstanding arrest warrants would be acted upon.
"One person that they had in custody they released about a year ago because they thought it was mistaken identity, then they decided it wasn't, so they reissued the arrest warrant.
"So obviously we were hoping that the whole thing was going to bring a lot more people in. But it's just not looking that way."
Charges against an eighth suspect were dropped earlier this year.
Mr Hyde's son Ben was a lance corporal from Northallerton, North Yorkshire.
The other Red Caps who died were Sgt Simon Hamilton-Jewell, 41, from Chessington, Surrey; Cpl Russell Aston, 30 from Swadlincote, Derbyshire; Cpl Paul Long, 24, from Tyne and Wear, L/Cpl Tom Keys, 20, from Bala, North Wales, and Cpl Simon Miller, 21, from Tyne and Wear.
They had been on a routine operation to train local police, and according to some reports had been playing football with the Iraqi police officers when a crowd of between 400 and 500 people attacked.
The six men were chased into a police station, where they were shot.
After local elders put out a request for witnesses, 16 people were initially arrested and charged.
A Ministry of Defence spokesman said Armed Forces Minister Nick Harvey had written to the men's families to inform them that five of the seven remaining suspects had seen their charges dropped.
Of the last two, one has still to be formally identified by Iraqi authorities.
An inquest into the Red Caps' killings in March 2006 found that the men had been given antiquated radios and inadequate ammunition.
But Coroner Nicholas Gardiner ruled that their deaths could not have been avoided.
However, the families of the men have called for an independent inquiry, arguing that negligence by Army personnel led to their deaths.