The Abu Ghraib prison abuse scandal has haunted the US mission in Iraq and cast a shadow over US President George W Bush's "global war on terrorism".
What are the main features of the scandal?
Allegations of severe maltreatment and abuse of Iraqi prisoners by US military and intelligence personnel and contractors at Baghdad's Abu Ghraib prison began emerging in 2003, prompting an internal US army investigation beginning in January 2004.
Abu Ghraib was a detention facility inherited from Saddam's regime
The Taguba report found soldiers had been committing "grave breaches of humanitarian law" in their treatment of prisoners. Seventeen soldiers and officers - including the camp commandant - were suspended and criminal proceedings were launched.
The abuse became public in April 2004 when CBS television and the New Yorker magazine published details of the abuse, including graphic photographs showing guards beating prisoners and forcing them into humiliating and stressful positions.
Senior members of the Bush administration, including the president, condemned the guards' behaviour as unrepresentative of the United States or its armed forces, although critics claim it was authorised at the highest level to "soften up" terrorism suspects.
Eleven members of the military have been found guilty of abuse or dereliction of duty and sentenced to up to 10 years' jail.
The prison commandant, Janis Karpinski, was demoted from the rank of general. She claims she was made a scapegoat by senior US staff in Iraq.
What is the nature of the abuse?
US courts martial have convicted former Abu Ghraib guards of assault, indecency, cruelty and forcing detainees to simulate lewd acts.
An intrinsic factor of the abuse seems to have been photographing the prisoners in their terror and suffering.
The images have become icons of anti-US anger (AP Photo/Courtesy of The New Yorker)
Dozens of digital photographs and grainy video clips have provided graphic and horrific evidence of what went on.
Scenes include prisoners being beaten, forced to strip and masturbate, threatened by unmuzzled dogs, smeared in faeces and made to simulate sex or form naked piles.
Other prisoners are reported to have been raped, sodomised and beaten to death.
Photographs were taken of bodies, sometimes with US troops grinning and doing thumbs-ups.
How has the US investigated the scandal?
After the initial report by Maj Gen Antonio Taguba, the US has held numerous investigations and congressional hearings into the allegations of abuse.
Two reports were published in August 2004 - the Schlesinger panel, led by former US Defence Secretary James Schlesinger and the Kern-Fay-Jones inquiry by the US army.
Both reports laid most of the blame on the soldiers involved and their local commanders, but each pointed a finger of criticism higher up.
According to the Fay report, 23 military intelligence personnel and four civilian contractors participated in or encouraged abuse at Abu Ghraib, some of which amounted to torture.
Six additional military intelligence soldiers and two contractors failed to report abuse, it says.
The report says senior officers like the former commander in Iraq, Lt Cdr Ricardo Sanchez, may be responsible for some of the problems at the jail - although they were not deemed directly culpable.
The Schlesinger report said chaos reigned at Abu Ghraib, and criticised the guards' "brutality and purposeless sadism", but also blamed senior uniformed staff in the Pentagon for not preventing the abuse.
Other reports included the Mikolashek report into training and prison procedures, the Church report into interrogation techniques and the Ertman report into the training of military police reserves.
Were senior commanders and political leaders implicated?
Schlesinger recommended Defence Secretary Donald Rumsfeld should not resign, as "his resignation would be a boon to all of America's enemies".
Mr Rumsfeld said he had twice offered to resign over the scandal, but both offers were refused by Mr Bush. Mr Rumsfeld has since left office, following Republican losses in the 2006 mid-term elections.
The president condemned the Abu Ghraib abuse, but was criticised for not apologising to the Iraqi people for it when he gave interviews to Arabic TV stations, including the US-owned al-Hurra.
The Senate Armed Services Committee asked the inspector-general to investigate the roles of five top officers including Gen Sanchez, his deputy Maj Gen Walter Wojdakowski and Gen Karpinski.
All of the officers were cleared of any wrongdoing except Gen Karpinski. She was relieved of her command and given a written reprimand.
What happened at the courts martial?
The first soldier to face court martial proceedings was Specialist Jeremy Sivits, a 24-year-old military policeman. He went on trial on 24 May 2004.
He admitted taking many of the pictures and pleaded guilty to abuse and conspiracy charges. He was given a one-year jail sentence and discharged from service.
Photographs were used as evidence against the abusers (AP Photo/Courtesy of The New Yorker)
Specialist Charles Graner Jr was said to be the ringleader of the abuser. He pleaded guilty and was sentenced to 10 years in prison, was demoted and given a dishonourable discharge.
He maintains that he was following the orders of military intelligence officers.
Staff Sgt Ivan L "Chip" Frederick II, Sgt Javal Davis, Specialist Roman Krol, Specialist Megan Ambuhl and Specialist Armin J Cruz Jr all pleaded guilty to charges relating to prisoner abuse, were sentenced to jail and discharged from the army.
Specialist Sabrina Harman was found guilty of abuse and given six months in prison. She alleged that her job was to keep detainees awake, including one hooded prisoner who was placed on a box with wires attached to his fingers, toes and genitals
Private Lynndie England - Graner's one-time girlfriend - was convicted for conspiracy, maltreating detainees and committing an indecent act, and jailed for three years. She also alleges she was following orders.
Dog handler Sgt Michael Smith received a six-month sentence for using his black Belgian shepherd to menace prisoners for his own amusement.
Lt-Col Steven Jordan, who headed the interrogation centre at the prison, was cleared of charges of cruelty to and maltreatment of detainees, but reprimanded for disobeying an order not to discuss the investigation. This was later thrown out by the US military authorities and replaced with an administrative reprimand, essentially a blot on his record.
Two of the most serious charges against him, of making a false official statement, and of lying under oath and obstructing justice, were dropped on a technicality.
How serious has the impact been?
The scandal dealt a serious blow to the US-led coalition's efforts to win over hearts and minds of the Iraqi people.
It has also had a powerful negative effect on the morale of US troops in Iraq.
The controversial images have been published in small batches over the months and years since early 2004, with the Pentagon doing its best to suppress some of the most sadistic scenes.
However, this has had the effect of stringing out the controversy to the detriment of US efforts to draw a line under the scandal.
UK soldiers have also been caught abusing prisoners - seen in a series of photos taken in Basra in May 2003 - damaging the credibility of the British military presence.
The Abu Ghraib images have been printed and broadcast around the world, fuelling anti-US anger and undermining Washington's claims to be bringing freedom and democracy to the Middle East.
The fact that Muslim men have been subjected to humiliation while naked has been particularly disturbing to audiences.
Some of the poses - such as the hooded, wired-up prisoner standing on a box - have become icons of anti-US feeling.