Working through the quite detailed and long sadism and torture report Inquiry Into the Treatment of Detainees in U.S. Custody" (pdf) the most significant admission to me is the footnote 1219 on page 158:

Notwithstanding differences between the legal status of detainees held in Iraq and those in Afghanistan, the [Special Mission Unit Task Force] used the same interrogation approaches in both theaters. In addition, the [Combined Joint Task Force 7] interrogation policies included techniques that had been authorized for use at GTMO. By September 2003, interrogation approaches initially authorized for a war in which the President had determined that the protections of the Geneva Conventions did not apply, would be authorized for all U.S. forces in Iraq.

Abu Ghraib was not an accident but official policy promoted from the very top and many people knew that.