The attorney general says he has concerns about the failed prosecution of British soldiers charged with the abuse of Iraqi civilians.
Hotel receptionist Baha Mousa died in custody in 2003
Lord Goldsmith told the BBC there were issues about the "capacity of the investigators" and the "lack of clarity" about detainee treatment.
All charges were dropped against four out of seven soldiers on trial over the allegations and two were later cleared.
The claims arose after the death of an Iraqi detainee in September 2003.
Lord Goldsmith told BBC Radio 4's Today programme he had "concerns about the capacity of the investigators" which he had raised with the Ministry of Defence (MoD) two years ago.
The investigation and trial took three years, with a reported cost of £20m - making it the UK's costliest ever court martial.
"We do need to be sure that the investigators have all the tools and the resources, not only to conduct professional and independent investigations, but to do so quickly and that's a point that's been made, I think, rightly by a number of people," Lord Goldsmith said.
He said that the trial also showed that there was an "apparent confusion" or "lack of clarity" about guidance given to troops regarding the treatment of detainees.
Col Jorge Mendonca was cleared of negligently performing a duty
"That's not fair to them, and it's not fair to the detainees, too," he added.
Last month, Col Jorge Mendonca, former commander of the Queen's Lancashire Regiment and the highest-ranking British serviceman in recent history to face court martial, had all charges dropped against him, along with three of his men.
And on Tuesday Maj Michael Peebles, 35, and Warrant Officer Mark Davies, 37, both of the Intelligence Corps, were cleared of negligently performing their duty.
The six-month court martial at Bulford Camp in Wiltshire dealt with claims the colonel's men abused a group of Iraqis arrested at a Basra hotel, which resulted in the death of hotel receptionist Baha Mousa, 26.
Cpl Donald Payne, 35, who admitted treating Iraqis inhumanely, is the only soldier to have been convicted at the end of the six-month hearing.
He was cleared of manslaughter and of perverting the course of justice and is awaiting sentencing.
In a statement to the BBC, the MoD said: "Investigating crime in Iraq is not without difficulty; given the significant cultural differences arising from the Islamic faith and the influence of tribal custom over and above the obvious language difficulties."
It added that the hostile operational environment added to the difficulties of conducting investigations.