Six years ago, FBI agents arrested one of their own, Robert Hanssen, accused of selling secrets to Moscow for some 15 years in what the Justice Department described as "possibly the worst intelligence disaster in U.S. History." The cat-and-mouse game leading up to Hanssen's arrest is dramatized in a new film co-starring Chris Cooper and Ryan Phillippe and Alan Silverman has this look at Breach.

In early 2001, Eric O'Neill is a young FBI operative conducting surveillance and other investigations while he works toward becoming an agent. When he's tapped for a special assignment, O'Neill believes it could take him closer to that goal.

Acting as Hanssen's assistant, O'Neill finds the veteran agent difficult and frustrating, but he sees nothing suspicious. When he complains to the agent managing the case, the young investigator learns the true reason for his assignment.

O'Neill's undercover work leads to Hanssen's arrest on charges of espionage and treason.

Today, Eric O'Neill is a Washington, D.C. attorney, but he remembers clearly the battle of wits with the turncoat agent.

"He did things to make me uncomfortable and keep me off-balance. If he kept me off-balance and in a place where I always was reacting to him then, in the end, he was going to win," ONeill recalls. "He was going to get me to trip up and say something that I shouldn't and then he would say 'oh, look, I am under investigation.' That was one of his goals: to see if that was indeed what was happening.

"I was able to get him to talk and then defend himself when he made assertions about counter-intelligence," he adds. "The more I forced him to defend himself, the more things came out that had to do with cases he should not have known about and that's when we really knew this is the spy."

Ryan Phillippe plays O'Neill in Breach and says having him on the set as a technical advisor gives the film a direct link to the true events.

"There is a responsibility to tell the man's story in the best way possible (and) do justice to the experience he had, but it does a lot of my work for me in some ways," he says. "A lot of times you're left to your own devices - your imagination - to create a character, but getting to know Eric and his personality gave me new ideas about how to play the part. I came into the rehearsal room with a completely different idea of how I was going to play this part. Sitting down and talking with him for a couple of hours completely changed things."

Chris Cooper, who plays Hanssen, says he also relied on O'Neill's memories because the real spy is now locked away in a maximum security prison. However, Cooper says he also had plenty of good research material.

"There's a lot of material on him. There are five books about him that go back to his childhood and are pretty in depth," Cooper says. " (We did) interviews with family, associates and neighbors; and when he was captured there was a psychological profile through his interrogation and the psychiatrists came up with a number of possibilities of 'why,' going back as far as the father-son relationship, which was pretty abusive."

Breach is written and directed by Billy Ray, who says he takes some dramatic license with the events, but not much.

"The story was pretty good. We didn't have to do a lot, but the litmus test you apply is 'are you being true to the spirit of the events?' " Ray explains.

Like Ray's first film as director - the 2003 fact-based drama Shattered Glass, about a journalist who fabricates his stories - this one also deals with a clash of ideals and betrayal of trust.

"I think liars make better characters. They are just more interesting to watch. Everything they do, you have to lean forward and pay close attention. They lend themselves to good storytelling," he says."For me, the movie is not actually about Hanssen. It is much more about Eric O'Neill and I think it's a movie about integrity, which is completely compelling to me. It is about this guy not quite knowing what the right thing to do is and then once he figures out what the right thing to do is, is he going to be able to do it? That was the story which actually took place with Eric."

Breach co-stars Laura Linney as the agent who puts O'Neill on the case. Kathleen Quinlan plays Hanssen's devout and devoted wife; and much of the film was shot on location in the Washington, D.C. area where the actual events took place.