Go read Scott's summary of the case and US resistance to admitting wrongdoing of any kind. He writes,
When the two inspectors general, Richard L. Skinner and Clark Kent Ervin, appeared before the House Judiciary Committee to testify on the matter, I was also invited as an independent expert. At one point, a committee member asked, “Is there sufficient basis to open a criminal investigation based on the conduct of the Justice Department in handling this case?” I stated that the evidence set out in the internal investigation showed that, after the immigration board concluded that Arar would likely be tortured in Syria, senior figures in the Justice Department had directed that he be sent there. This presents all the elements of a prima facie conspiracy to torture under the criminal code. Both inspectors general concurred that a criminal investigation was now warranted. Their own report produced ample evidence of gross departures from established procedures, as well as evidence that the entire case was being politically micromanaged by political figures in the attorney general’s office and in the White House, who repeatedly overrode the decisions of the professional staff. Attorney General Mukasey, however, subsequently declined to direct the investigation. It’s noteworthy that the investigation would have focused on the attorney general’s own office, which raises fair questions about why the attorney general would be the person making this decision.Note that there's little incentive from past and possibly current US officials to prosecute such cases. When a government is bound up with investigating its own crimes and ethics violations, and those who would carry out the investigations would likely also be subject to the investigations, and thus refuse to follow the conclusions of independent legal experts, you essentially have the basic framework of corruption. This is the kind of corruption that does not get rooted out. Add that to the list of the effects of the torture regime.