The death of innocent Iraqi Baha Mousa "cast a dark shadow" over the British Army's reputation, its head said today.
General Sir Peter Wall said soldiers were now "in no doubt about the need to treat detainees humanely and with respect" and "had that been the case in Basra in 2003, Baha Mousa would not have died in British custody".
Sir Peter said: "The shameful circumstances of Baha Mousa's death have cast a dark shadow on that reputation and this must not happen again."
The victim died at the hands of soldiers from the First Battalion, the Queen's Lancashire Regiment, who took him into custody from the Ibn Al Haitham hotel where he worked as an overnight receptionist.
His abuse and death sent shockwaves through the Army, resulting in seven 1QLR soldiers, including the battalion's former commanding officer Jorge Mendonca, being court martialled in 2006/07.
The trial ended with them all being cleared except Corporal Donald Payne, who pleaded guilty to inhumanely treating civilians.
Defence Secretary Liam Fox has asked Sir Peter to consider, where individuals are still serving, what action can be taken against them.
And the officer said he would take the lead in implementing recommendations from Sir William Gage, chairman of the Baha Mousa public inquiry and accompanying report author.
Sir Peter said: "The Army has apologised unreservedly to Baha Mousa's family and to the surviving victims of this shocking episode.
"And I would like to take this opportunity to repeat that apology today."
He added: "Both at home and on operations the Army must act within the law.
"It must prepare for and conduct operations in accordance with our core ethos and it must behave properly, particularly in demonstrating respect for others."
Sir Peter went on: "The nation places its trust in us and we expect our soldiers' conduct to reflect that trust, no matter how challenging the environment may be.
"Our operational effectiveness depends on this and we expect commanders at all levels to lead by example.
"We also expect our soldiers, no matter how junior, to understand the clear distinction between right and wrong in the heat of the moment.
"This did not happen in the case of Baha Mousa and others."
He added there could be no excuse for "the loss of discipline and lack of moral courage that occurred."
The top officer said the Army was unprepared for dealing with civilian prisoners but has made improvements since 2003.
Sir Peter said he was confident all soldiers deployed today were "fully trained in their legal responsibilities and can be in no doubt about the need to treat detainees humanely and with respect".