The story that Sgt. Erik Saar, a soldier who spent three months in the interrogation rooms at Guantanamo Bay, Cuba, tells paints a picture of bizarre, even sadistic, treatment of detainees in the American prison camp.

Experts in intelligence tell 60 Minutes that if what Saar says is true, some soldiers at Guantanamo have undermined the war on terror, bungling the interrogation of important prisoners.

60 Minutes also reveals previously secret emails from FBI agents at Guantanamo that warn FBI headquarters that prisoners are being tortured.

"I think the harm we are doing there far outweighs the good, and I believe it's inconsistent with American values," says Saar. "In fact, I think it's fair to say that it's the moral antithesis of what we want to stand for as a country."

Saar volunteered for Guantanamo Bay in 2002. He was a U.S. Army linguist, an expert in Arabic, with a top-secret security clearance. He was assigned to translate during interrogations. The prisoners, about 600 in all, were mostly from the battlefields of Afghanistan. And Saar couldn't wait to get at them after what the administration said: the men were "among the most dangerous, best-trained, vicious killers on the face of the earth."

With that in mind, Saar went to work, but he was surprised by what he found.

How many prisoners did he think were the worst of the worst – real terrorists?

"At best, I would say there were a few dozen," says Saar. "A few dozen [out of 600]."

Who were the rest of the guys? "Some of them were conscripts who actually were forced to fight for the Taliban, so actually had taken up arms against us, but had little or no choice in the matter," says Saar. "Some of them were individuals who were picked up by the Northern Alliance, and we have no idea why they were there, and we didn't know exactly what their connections were to terrorism."

However they got there, Saar and the rest of Guantanamo's intelligence personnel were told that the captives were not prisoners of war, and therefore, were not protected by the Geneva Convention.

"Your training in intelligence had told you what about the Geneva Conventions?" asks Pelley.

"That they were never to be violated," says Saar. "As a matter of fact, the training for interrogators themselves, their entire coursework falls under the umbrella of you never violate the Geneva Conventions."

"If the rules of the Geneva Convention did not apply, what rules did apply?" asks Pelley.

"I don't think anybody knew that," says Saar.

And so, Saar said, some U.S. military intelligence personnel used cruelty, and even bizarre sexual tactics against the prisoners. Saar has written a book, "Inside the Wire," about his experiences at Guantanamo. Penguin Press will release it on Tuesday.

He told 60 Minutes about one interrogation in particular, in which he translated for a female interrogator who was trying to break a high-priority prisoner — a Saudi who had been in flight school in the United States.

"As she stood in front of him, she slowly started to unbutton her Army blouse. She had on underneath the Army blouse a tight brown Army T-shirt, touched her breasts, and said, 'Don't you like these big American breasts?'" says Saar. "She wanted to create a barrier between this detainee and his faith, and if she could somehow sexually entice him, he would feel unclean in an Islamic way, he would not be able to pray and go before his God and gain that strength, so the next day, maybe he would be able to start cooperating, start talking to her."

But the prisoner wasn't talking, so Saar said the interrogator increased the pressure.

"She started to unbutton her pants and reached and put her hands in her pants and then started to circle around the detainee. And when she had her hands in her pants, apparently she used something to put what appeared to be menstrual blood on her hand, but in fact was ink," says Saar.

"When she circled around the detainee, she pulled out her hand, which was red, and said, 'I'm actually menstruating right now, and I'm touching you. Does that please your God? Does that please Allah?' And then he kind of got pent up and shied away from her, and she then took the ink and wiped it on his face, and said, 'How do you like that?'"