But with polygraphs often setting off false alarms, what are the chances of branding innocent people as traitors? Navy Petty Officer Daniel King says that happened to him. After King took a routine polygraph test, the Navy accused him of espionage and kept him in jail for over a year and a half - without having any physical evidence of a crime. The Navy won't speak publicly about the case but Daniel King recently spoke with Correspondent Vicki Mabrey.
King denies spying or having any contact with a foreign embassy or with foreigners regarding any classified information.
But the United States Navy did not believe Daniel King - even though by all accounts he was a model sailor. After 18 years of service, King was a cryptologist working on some of the Navy's most classified operations.
But with his tour of duty in Guam coming to an end in the fall of 1999, King - like all Navy specialists with top secret clearance - took a routine polygraph in order to transfer back to the states.
What happened next was "the beginning of a nightmare," he says. "What I found out was that I came up indeterminate on one of the questions."
He can't remember the actual question. "And I don't think that they actually ever told me what question I came up indeterminate on," he says.
An indeterminate polygraph doesn't mean King failed that first test; it means the examiner couldn't determine whether he was lying. So he was brought back the next day and retested several times. The Navy says that in later tests some of King's responses indicated deception.
"It eventually got to be where I heard somebody say spy, and I'm...wondering what's going on," King says.
King was taken into custody and interrogated around the clock by agents from the Naval Criminal Investigative Service.
"That's when I started getting interrogated for 17 to 19 hour at a time," he says. "When we'd get done, I'd go back to the safe house and go into a room. I'd have to leave the door open, the lights would be on, they'd blare the TV, the phone would keep ringing all the time. Even when I went to the bathroom, I had to leave the door open."
Two people grilled him for hours for 26 days, King says. And during that time, King did not see a lawyer. The Navy says he never asked for one. King did repeatedly waive his right to a lawyer - although a document shows that on at least one occasion, he requested one.
Numerous times he was asked if he was a spy and he denied it, King says. "Then when I didn't give them the answers they wanted, they became irritated, and the questions became statements."
He recalls an exchange: "'Danny, we know you sent a disk to the Russian Embassy.' And I'd go, 'No, I didn't.' Then they'd just go on at length sometimes just hammering points, like 'We know you're a spy. We know you're committing espionage.'"
King says he became so confused during the interrogations he was not sure whether he had committed espionage or not. The audiotapes from the interrogations have been classified.
But 60 Minutes II obtained a recently de-classified videotape - not of the interrogations, but of King asking NCIS psychologist Michael Geles for sodium pentothal, or truth serum, to help him remember if he had done anything wrong.
With other NCIS agents sitting off camera, King told Geles he was so confused he can't tell dreams from reality.
One time when King was nodding off, officials woke him up and asked him what was he dreaming about, he recalls. "I was dreaming about being married to a beautiful woman on the Russian Black Sea," he says.
"They started writing it down," King says. Even though he said it was just a dream, he was told, "If you're dreaming it, you're thinking it; it must be real," according to King.
"What the NCIS did to this guy comes out of a bad dime novel," says George Washington University Law Professor Jonathan Turley, who specializes in national security cases. He currently represents King. "They did everything but beat this guy with a chair."
"If you interrogate someone for 19-hour stretches, you can eventually get anyone to say they're a rhinoceros," Turley says. "If I put you through 28 days of interrogation with 19-hour stretches, I could get you to admit anything, because at some point you lose the resistance. You just want it to stop."
That's what King says happened to him on the eighth day of questioning. After being interrogated for 30 hours over a two-day period, King gave the NCIS agents what they were looking for: a confession.
So King signed a statement that said that he sent a disk to the Russian embassy, he says. King says he indicated, "This is not true. I'm just giving this to you because I want this to be over." His rationale: If he could get away from the people who wouldn't give him a lawyer, the truth would come out.
NCIS refused 60 Minutes II's request for an interview but sent a letter saying King admitted to wanting to "hurt the Navy" and to committing "serious security violations." It says King was never "coerced."
After leaving NCIS custody, King was transferred to the brig at Quantico, Va., where he waited for more than a year while the Navy to built its case against him. In the search for evidence, the Navy sent investigators across the globe and interviewed hundreds of people associated with King.
"Proving an espionage case is one of the most difficult investigations for any law enforcement officer," says David Major, who helped run the FBI's spycatching operation for 20 years. "You're looking at a case that almost always (is) a circumstantial case, a case in which you have to put the pieces together. It becomes an analytical puzzle, and very seldom do you actually prove a case by catching somebody in the act."
And the case is even more difficult when it is based on a confession, Major says. "There are examples where innocent people confess. In fact that's one of the reasons the law is written in such a way that you have to independently corroborate information in the confession."
King's Navy-appointed lawyers, JAG Lieutenants Matthew Freedus and Robert Bailey, reviewed the government's evidence against King after they were assigned as defense attorneys.
It quickly became clear the government did not have a case, Bailey says. "The government raided every aspect of Petty Officer King's life," he says. "They have his sheets in a box labeled 'evidence' in the NCIS locker....There's no evidence he traveled extensively.... No evidence that he ever obtained any money....They searched everything, found nothing."
Bailey estimates that the government spent millions looking for a spy. "They found somebody they were able to coerce into a confession," he says.
Turley, who joined Bailey on the King case more than a yer ago, blames the Navy for trying to build a spy case around an indeterminate polygraph. "It is very common for people to come up indeterminate on polygraphs. It's even common to have false negatives. And, by the way, real spies often have little trouble passing polygraphs. Aldrich Ames passed a polygraph. And so when you are a pathological liar, or a traitor, you often have a better shot than if you are a petty officer on a bad day."
After 520 days, the Navy dropped the charges against Petty Officer Daniel King. In a strongly worded "Recommendation for Dismissal," the investigating officer said there was reason to believe that King's confession may have been coerced and that "the investigation did not reveal any direct evidence to corroborate the accused's confession."
"Soon after the man was detained, the Navy billed this case (as) a counterintelligence coup," Turley says. "After that happened, various people in the Pentagon realized they didn't have a spy. But nobody had the integrity to admit the error. So they left this guy to rot in jail."
Did the U.S. Navy hold an innocent man for more than 500 days or did the Navy let a spy go? "We're not in a position to make that judgment," Major says. "It shows the complexity of espionage, why it's so difficult to prove these cases. And if you make a mistake, you're going to be second guessed....Time, hopefully will tell us what we have."
The Navy defends its actions. In a letter to 60 Minutes II, officials write that it is "regrettable" that Petty Officer King spent more than a year in "pre-trial confinement," but that "the majority of that time was due to legal tactics employed by King's defense team." And that given his "failed polygraphs" and "incriminating statements," the government had an "obligation to investigate."
King says the hardest thing about his confinement was that his mother died. "My sister told me that her last words were I don't know if my son is going to be executed or not, but I know he's innocent," he says.
After his release two weeks ago, King was reunited with his daughter. And he met his 6-month-old grandson for the first time. Next month King will be honorably discharged from the Navy after 20 years of service. He has returned to his hometown in Ohio where he will do a tour of duty in the family bakery.
"I never lost faith in the Navy," King says. "The Navy, to me, (is) those men and women that I served with. The people who did this are not the men and the women that I served with in the Navy.
"I love my country. I love the people that I served with. I loved my job and I would do it again," King adds.