Enough evidence has been gathered against suspects in the murder of six military policemen to take the case forward, the Prime Minister has said.
The men were surrounded by a mob and killed
Tony Blair said it would be unacceptable if the Red Caps' killers were pardoned in an amnesty proposed by the Iraqi interim government.
The Ministry of Defence has asked the Iraqi Central Criminal Court to investigate the deaths.
The files on the deaths of the Red Caps have been given to the Iraqi court.
At Parliamentary question time on Wednesday, Plaid Cymru's Elfin Llwyd said: "My constituents, the parents of the late Lance Corporal Tom Keys, are very concerned that the court will not proceed with the investigations."
Lance Cpl Keys died just four days before his 21st birthday alongside five other Red Caps who were defending a police station 120 miles north of Basra.
The military policemen were killed on 24 June last year after being surrounded by more than 400 protesting Iraqis.
RED CAPS KILLED IN IRAQ
Corporal Simon Miller, 21
Sergeant Simon Alexander Hamilton-Jewell, 41
from Chessington, Surrey
Corporal Russell Aston, 30
Corporal Paul Graham Long, 24
Lance-Corporal Benjamin John McGowan Hyde, 23
Lance-Corporal Thomas Richard Keys, 20
Bala, N Wales
Mr Llwyd was also concerned about any potential amnesty for insurgents.
"Would you intervene personally to ensure that the investigation proceeds to a fair conclusion, especially since suspects' names are known?" he asked.
The father of a South Derbyshire soldier killed in the ambush backed the Prime Minister's call for the killers to be brought to justice.
Corporal Russell Aston from Newhall, was among the Red Caps killed defending a police station last June.
Cpl Aston's father Mike says he is still not convinced a trial will happen.