Indeed, as legal experts have pointed out, and 9/11 Commission Director Zelikow tacitly acknowledges, evidence based on torture is not reliable. As the NBC news report states:

"We were not aware, but we guessed, that things like that were going on," Philip Zelikow, the 9/11 Commission executive director, told NBC News. "We were wary…we tried to find different sources to enhance our credibility."

Specifically, the NBC News analysis shows 441 of the more than 1,700 footnotes in the Commission’s Final Report refer to the CIA interrogations. Moreover, most of the information in Chapters 5, 6 and 7 of the Report came from the interrogations. Those chapters cover the initial planning for the attack, the assembling of terrorist cells, and the arrival of the hijackers in the U.S. In total, the Commission relied on more than 100 interrogation reports produced by the CIA. The second round of interrogations sought by the Commission involved more than 30 separate interrogation sessions.

No one disputes that the interrogations were critical to the Commission’s understanding of the plot.,,

Zelikow said the lack of direct access forced the Commission to seek secondary sources and to request the new round of questioning. In the end, says Zelikow, the Commission relied heavily on the information derived from the interrogations, but remained skeptical of it. Zelikow admits that "quite a bit, if not most" of its information on the 9/11 conspiracy "did come from the interrogations."

"We didn’t have blind faith," Zelikow tells NBC News. "We therefore had skepticism. The problems (in getting cooperation from the agency) enforced our concerns about the underlying interrogation.

A former senior U.S. intelligence official says the Commission never expressed any concerns about techniques and even pushed for the new round...

Commission staffers interviewed by NBC News do not dispute the official’s assertion that they didn’t ask about interrogation techniques. "We did not delve deeply into the question of the treatment of the prisoners", as one put it. "Standards of treatment were not part of our mission." According to the other, "We did not ask specifically. It was not in our mandate."...

Michael Ratner, president of the Center for Constitutional Rights, says he is "shocked" that the Commission never asked about extreme interrogation measures.

"If you’re sitting at the 9/11 Commission, with all the high-powered lawyers on the Commission and on the staff, first you ask what happened rather than guess," said Ratner, whose center represents detainees at Guantanamo. "Most people look at the 9/11 Commission Report as a trusted historical document. If their conclusions were supported by information gained from torture, therefore their conclusions are suspect."...

Zelikow adds that one particularly telling position was the agency’s refusal to let the Commission interview the interrogators.

"We needed more information to judge reports we were reading," he said. "We needed information about demeanor of the detainees. We needed more information on the content, context, character of the interrogations."...

Ratner argues "if they suspected there was torture, they should have realized that as a matter of law, evidence derived from torture is not reliable, in part because of the possibility of false confession…at the very least, they should have added caveats to all those references."...

See also this, this, this, this and this.