Second, it lays to rest the notion that any sort of thorough investigation up the chain of command from the low-level personnel who actually abused prisoners at Abu Ghraib ever took place:
Rumsfeld was particularly concerned about how the classified report had become public. "General," he asked, "who do you think leaked the report?" Taguba responded that perhaps a senior military leader who knew about the investigation had done so. "It was just my speculation," he recalled. "Rumsfeld didn’t say anything." (I did not meet Taguba until mid-2006 and obtained his report elsewhere.) Rumsfeld also complained about not being given the information he needed. "Here I am," Taguba recalled Rumsfeld saying, "just a Secretary of Defense, and we have not seen a copy of your report. I have not seen the photographs, and I have to testify to Congress tomorrow and talk about this." As Rumsfeld spoke, Taguba said, "He’s looking at me. It was a statement."
Taguba filed his report in March. In it he found "Numerous incidents of sadistic, blatant, and wanton criminal abuses were inflicted on several detainees ... systemic and illegal abuse." ... “From what I knew, troops just don’t take it upon themselves to initiate what they did without any form of knowledge of the higher-ups,” Taguba told me. His orders were clear, however: he was to investigate only the military police at Abu Ghraib, and not those above them in the chain of command. “These M.P. troops were not that creative,” he said. “Somebody was giving them guidance, but I was legally prevented from further investigation into higher authority. I was limited to a box.”
Whether the President was told about Abu Ghraib in January (when e-mails informed the Pentagon of the seriousness of the abuses and of the existence of photographs) or in March (when Taguba filed his report), Bush made no known effort to forcefully address the treatment of prisoners before the scandal became public, or to reëvaluate the training of military police and interrogators, or the practices of the task forces that he had authorized. Instead, Bush acquiesced in the prosecution of a few lower-level soldiers. The President’s failure to act decisively resonated through the military chain of command: aggressive prosecution of crimes against detainees was not conducive to a successful career.
Seymour Hersh's article is here, and Dan Froomkin at The Washington Post provides an excellent analysis with some supplementary information here.