Albert Woodfox lived alone with his own fears for the 43 years he spent isolated behind bars — his story is just one of the many stories of people who have been locked up in solitary confinement.

Nearly 20 percent of all prison inmates and 18 percent of jail inmates said they had spent time in solitary, according to BJS numbers. But the practice has drawn increased levels of scrutiny in recent years, as research and high-profile reform initiatives shed light on an ugly facet of U.S. criminal justice.

Still, testimony from formerly incarcerated people who spent significant time in solitary confinement provides a uniquely chilling indictment of the practice. Here's what each of the Angola 3 — who together spent more than 110 years in small, isolated cells — have said about the practice over the years.

Albert Woodfox, 43 years in solitary confinement

International Coalition to Free the Angola 3/AP - msnbc.com

Woodfox was finally released on February 19 and is one of the so-called "Angola 3," a group of three prisoners known for the decades they spent in solitary lock up at a Louisiana prison colloquially named for the slave plantation it was built on. The 69-year-old is the last of the three to be released.

Following his release, Woodfox said he would devote efforts to ending the use of solitary confinement, the horrors of which he is all too familiar.

"It's an evil. Solitary confinement is the most torturous experience a human being can be put through in prison. It's punishment without ending," he told the Guardian. "We have got to stop this, and having been a victim of it for so long myself, that's what I'm going to do."

In 2014, Woodfox told a blogger of the fears he experienced while in solitary lock up.

"I'm afraid I'm going to turn into a baby and curl up in a fetal position and lay there like that day after day for the rest of my life. I'm afraid I'm going to attack my own body, maybe cut off my balls and throw them through the bars the way I've seen others do when they couldn't take any more."

Herman Wallace, 41 years in solitary confinement

Innocence Project/ The Advocate - nytimes.com

Wallace was released in October of 2013, and died of cancer less than a week after he was released. According to a statement from Wallace's legal team, the 71-year-old hoped that solitary confinement litigation tied to his case "will help ensure that others, including his lifelong friend and fellow 'Angola 3' member, Albert Woodfox, do not continue to suffer such cruel and unusual confinement[.]"

"I am free," Wallace said on his death bed, according to friends and family. "I am free."

"When you speak about torture, you're speaking about a torture of the mind," Wallace said in a 2013 radio interview about his time in solitary.

Robert King, 29 years in solitary confinement

CNN - cnn.com

King, the third Angola 3 member, was released in 2001. Since then, he has been vocal in condemning solitary confinement, including conducting a TEDx Talk, and authoring a book on his time in prison.

"Some wanted to know, 'Well why didn't you go crazy?'" King told a crowd gathered for his TEDx talk about his time in solitary. "I let them know, 'I did not tell you I was sane,'" he joked. "It's impossible to get dipped in waste and not come up stinky."

"You don't cry tears, you don't cry literally; you cry with your soul and it's kind of hard to describe when the soul cries," King said in a documentary about the Angola 3. "I mean it's a deep — it's an agony, you know?"