Lee Boyd Malvo said he remembers each of the sniper shootings in detail. But one moment – one image – stands out among the carnage of that terrifying time 10 years ago: "Mr Franklin's eyes." Malvo remembers being in the blue Chevrolet Caprice.

He scanned the area to make sure John Allen Muhammad had a clean shot. He gave the "go" order and looked across Route 50 at the target. Muhammad, hidden on a hill above, pulled the trigger. A bullet screamed across the highway, instantly killing Linda Franklin, who had been going about her business at a shop in Seven Corners, Virginia, at precisely the wrong time.

He remembers her husband Ted Franklin's eyes – the devastation, the shock, the sadness after the shot. "They are penetrating," Malvo said in a rare media interview from prison.

"It is the worst sort of pain I have ever seen in my life. His eyes… Words do not possess the depth in which to fully convey that emotion and what I felt when I saw it… You feel like the worst piece of scum on the planet."

It has been 10 years since Malvo and Muhammad went on one of the most notorious killing sprees in America's history. Over 21 days in October 2002, the pair ambushed 13 unsuspecting strangers, killing 10 of them, in the Washington area. They succeeded in terrorising the region, as death could come anywhere, anytime: in gas stations and car parks. They even wounded a 13-year-old standing in front of school.

After the two were caught, they were tied to at least 11 more shootings from Washington state to Alabama, five of them fatal. Muhammad is gone – executed in 2009 for his crimes. Malvo, the scrawny teenager and cold-blooded accomplice, is now 27.

He speaks with animation and poise, and with an adult perspective on what he did. He claims to understand the enormity of his actions – the trail of death and loss and pain he left behind.

"I was a monster," Malvo said. "If you look up the definition, that's what a monster is. I was a ghoul. I was a thief. I stole people's lives. I did someone else's bidding just because they said so... there is no rhyme or reason or sense."

Retired FBI agent Brad Garrett, who helped question Malvo in 2002, said he's not surprised by what Malvo is saying now in 2012. "When we interviewed him, our belief was that he was under the spell of Muhammad and that would wear off as time went on," Mr Garrett said.

Malvo is confined to a small, segregation cell for 23 hours a day – he gets to exercise in an enclosed pen, take showers and sometimes do menial jobs on his own during that other hour. He has no physical interaction with other inmates. He has taken a deep interest in yoga and meditation. Malvo said he has had to work hard to recover from what he calls a total brainwashing at the hands of a "sinister" and "evil" man who manipulated him into an effective "killing machine".

Jurors spared Malvo's life, largely because they believed that while he was responsible for the killings, he was also under Muhammad's control. Malvo grew up in Jamaica and Antigua, and he looks back at the 14-year-old who met Muhammad as if he's a million miles away. That boy was bouncing from his father to his mother and enduring physical abuse.

"The groundwork was laid in Antigua because I leaned on him, I trusted him," Malvo said. "I was unable to distinguish between Muhammad the father I had wanted, and Muhammad the nervous wreck."

Malvo said that Muhammad had him go to a gun range nearly every day, where he learned how to shoot dozens of different weapons. Muhammad would lurk over Malvo's shoulder and tell him to envision himself shooting and killing the old Lee Malvo, the weak Lee Malvo.

So Malvo shot at himself, over and over and over again. When it came time for the first killing – Kenya Cook, 21, in Tacoma in February 2002 – Malvo said it was almost automatic. He saw his own face on Ms Cook's and was thinking he shot himself. He said he doesn't even remember what she looked like. He vomited later, racked with grief.

"That was the beginning of the end," Malvo said. "I knew I was going to die one way or the other, that going down this path ended with my death."

Malvo said there were several times when he thought about killing himself and once when he pulled a gun on Muhammad. He also said there was one time he drew a line: Muhammad told Malvo he had to kill a pregnant woman, and Malvo couldn't bring himself to do it.

Malvo said the most enduring memory about the shootings for him, next to Ted Franklin's eyes, is something he realised when he returned to Virginia after testifying against Muhammad in Maryland. He saw a television show in which Stanton Samenow - a clinical psychologist – explained that a criminal's actions do not devastate just a family but also their whole community.

"Once I began to list the victims for every single possible crime that I could think of, the number, quickly, it was like multiplying by seven. It just exponentially grew," Malvo said. "The enormity of it. When you're in the midst of doing the shooting, that was my sole focus. I didn't give it thought… You never get a grasp on what the ramifications were for others."

Malvo is outwardly apologetic to his victims and their families. When asked what he would say directly to them, he implored people to forget about him.

"We can never change what happened," Malvo said. "There's nothing that I can say except don't allow me and my actions to continue to victimise you for the rest of your life. It may sound cold, but it's not. It's the only sound thing I can offer. You and you alone have the power to control that. And, you take the power away from this other person, this monster, and you take control…"