Malvo, 27, told NBC's "Today" from the age of 15 until he was arrested two years later for the shootings, he was abused by John Allen Muhammad.
"I felt a sense of shame, and I just said, 'That's just something that I'd never tell anyone.' And to a certain extent, up until that point, I really couldn't handle it," he said.
Malvo, who was 17 at the time of the shootings, said he was under the spell of Muhammad, who controlled what he ate, when he slept, what he read and his itinerary. The two had met in Antigua where Malvo was bouncing between living with his mother and father, and where he said he was subjected to abuse, he told The Washington Post last month.
He said he's coming forward about his abuse now because he feels he is more mature.
"As far as the guilt that I carried around for several years, I dealt with that to a large extent for years. And now, I can handle this," he said.
Malvo also told "Today" there were more victims of his shooting spree than have been identified so far, and he has contacted some of the families of those victims.
"Without anyone contacting me 2 1/2 years ago, I reached out and I did that. In five different instances in different states. But there was a point in time where psychologically, I couldn't handle it ... I cannot afford to break down psychologically in here because there will be no help," Malvo said.
Malvo is serving a life sentence at Red Onion prison in Virginia for his role in the shootings. Muhammad was executed in 2009.
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