It was a year ago this week that pictures from Abu Ghraib prison in Iraq horrified the world.

In the United States, the reaction to the horrible tale of abuse, torture and humiliation of Iraqi prisoners at the hands of U.S. soldiers prompted bipartisan outrage and calls for immediate answers.

We know a lot more now than we did last year when “60 Minutes” first took the country inside Abu Ghraib. But the anger has faded to quiet acceptance and a government whitewash.

At first, the terrible crimes committed at Abu Ghraib were portrayed as the deranged acts of a few low-level GIs, out of control and acting on their own. But the exposed events at the Baghdad prison turned out to be just the tip of the iceberg.

Abuse – and in many cases torture – were systematic throughout U.S. detention centers utilized in the war on terror. Often, poorly trained soldiers were in charge of interrogating and controlling prisoners with the only order being to get results.

Beginning in the highest levels of the Bush administration, illegal interrogation tactics were legitimized and spread like a virus down the chain of command, jumping from Guantanamo Bay – where alleged al-Qaida operatives are still held – to prisons in Iraq, Afghanistan and secret locations around the world.

At least 28 prisoners have died in U.S. custody in cases regarded as criminal homicide. More than 100 more have died while in detention.

According to Human Rights Watch, there have been more than 300 investigations into abuse, and 137 soldiers have been punished. Of those, 76 received administrative, nonjudicial punishments. The highest-ranking officer punished so far is Marine Maj. Clarke Paulus, who was found guilty of maltreatment and dereliction of duty in connection with a prisoner’s death. He was dismissed from the Marines.

While abuse was systematic, the investigations and punishment have been anything but. No senior-level officers have been punished, and the members of the Bush administration most closely associated with the abuse scandal have been honored or promoted, including now-Attorney General Alberto Gonzales. Multiple investigations have shown that senior-level officials are culpable, that their actions and inactions led to the abuse, and that they were slow to react once questionable tactics were discovered.

Accountability cannot rest solely on the shoulders of soldiers in the field. An independent and thorough investigation of the prisoner abuse, interrogation tactics and the rendering of detainees to other countries is needed.

The conscience of the country will not be clear until those responsible for criminal behavior against prisoners are held accountable.