Here, as posted on this forum many times already:
http://corner.nationalreview.com/post/?q=ZDE5YTNmZTg5OWUyOTlkMGUxOTk3OGMxY2I4ZDQ4YWQ=
Summarizing the facts claimed in it one could say ...
1) On 9/11 a terrorist plot horrifically murdered over 3000 innocent men, women and children in the United States.
2) We captured the mastermind of that plot, a man with the initials KSM. He was a man so evil that he actually plotted the death of 30,000 people and managed to murder over 3000.
3) KSM was interrogated by conventional means and yes, he did reveal some information, but apparently nothing that he didn't already think we knew. They were totally unable to get him to reveal information about any ongoing or still planned plots, and he did not give up the names of any other terrorists that he thought we didn't already know.
4) When asked what al-Qaeda plots were in the works, KSM told the interrogators that "Soon, you will know". So here was a terrorist, who they already knew had masterminded the killing of 3000+ people in a horrific manner; who destroyed four commercial passenger jets and a complex of skyscrapers to do it; who caused a trillion dollars in damage to an economy overall; and who damaged the psyche of an entire nation, and he was leading investigators to believe that "soon" there would be other such calamities.
5) And those investigators knew that there were indeed other plots underway. They knew that the terrorist organization was large, with many members. They knew that KSM was high enough in the al-Qaeda organization to know about some of the plots. In fact, they'd already discovered that he looked into crop dusters before he was caught ... planes whose only terrorist use might be to spread some form or biological or chemical weapon, which it was feared they might have obtained. So if nothing else, they suspected that might be an ongoing plot.
6) So they decided to waterboard him. And after getting nothing out of KSM by conventional interrogation, that he didn't think they already knew, he broke in minutes and started telling them things about ongoing plots and the names of other terrorists. Sure, he continued to resist, week they learned many things that indeed did prevent the loss of many additional lives (and not just Americans).
7) The article I linked lists some of the life saving facts they learned from waterboarding KSM and the two other top al-Qaeda members. As result of the information they obtained, they captured multiple additional terrorists ... terrorists who they hadn't known anything about even after months of conventional interrogation ... terrorists who were actively plotting additional mass murders at the time they were caught ... terrorists who were involved in the mass murder plots that had already taken place or that had been involved in plots that had been stopped.
8) And as pointed out in that article, one the plots (carrying out simultaneous attacks on the consulate, western residences and westerners at the local airport in Karachi) was stopped only days before it was completed. And the only reason that happened is that we used enhanced interrogation techniques on another captive.