Mother Jones reporter Shane Bauer has spent much of his career reporting on criminal justice. For years he’d been frustrated by the secretive nature of the American private prison industry. Tired of old-fashioned document-hunting, he tried an unconventional approach. He went undercover, spending four months as a prison guard at Winn Correctional Center in Winnfield, Louisiana.

His 35,000-word story provides a rare, harrowing look at the closed world of private prisons — a system that holds 131,000 people nationwide. What he saw still haunts him: men stabbing each other with handmade knives as guards looked on; officers in tactical gear storming the prison’s dormitories; an assault victim writhing in panic as he pleaded for protection from a predatory inmate; a prisoner whose gangrene went untreated so long he had to have his legs amputated.

But of all the alarming things Bauer experienced, perhaps the most frightening was the transformation he noticed within himself. He entered the system intent on being a passive observer— a diligent reporter disguised as a laid-back, upstanding guard. But in time, he became aggressive, even vindictive, toward the prisoners. He squabbled with the men and sought reasons to punish them. His anger and paranoia metastasized and scared him.

“I wonder who I am becoming,” he wrote in the piece. “I feel ashamed of my lack of self-control, my growing thirst for punishment and vengeance. I’m getting afraid of the expanding distance between the person I am at home and the one behind the wire.”

Bauer had once been a prisoner himself. He was held captive in an Iranian prison for some 26 months during his time as a freelance correspondent in Syria in 2009. He spent four of those months in solitary confinement. But as a guard, he had to send men to what was known as “the dungeon” — Winn Correctional’s dreaded segregation unit.

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Today, more than a year after his stint as a guard, he joins the ProPublica podcast and speaks candidly about his prison life. Here are some highlights from our conversation:

Sapien: It seems clear that you enter the prison at a time of crisis. What precipitated that and how did it influence the job?

Bauer: While I was in training, there was an escape. A man just, in the middle of the day, climbed over the fence in view of the guard towers and ran into the woods. Nobody saw him, partially because there's no guards in the towers anymore. The company had removed those posts. They replaced them with cameras, presumably to save money. People didn't even know that he escaped for a few hours. That drew a lot of attention from the state. There were also a lot of stabbings. I witness stabbings myself, saw people get beaten. There were weeks that had multiple stabbings just in one week. It had the sense of getting out of control. The prison was locked down several times when I was there, which always raised the frustration level of the prisoners because they would just be stuck in their dorms. There was one time that they had been on lock down after a rash of stabbings for over a week, for 11 days, I think, and the prisoners in my unit threatened to riot.

Sapien: One thing that I think many investigative journalists struggle with is that some of the horrific things that we see make for great stories. The revelations are powerful, but at the same time, they're profoundly depressing. You must've felt that in an even more acute way considering that you'd experienced some of it yourself as a former prisoner. Can you walk us through what was happening for you internally over the course of these 4 months?

Bauer: Yeah, it was hard for me, really, to see the extent of it until I left. I was aware of how I was changing in the prison and how I was relating to prisoners differently and how I was turning off emotionally in order to cope with the situation. My wife came a couple of times for extended visits in Louisiana, and on her second time down, she told me, "You're changing." I was having nightmares at night. I was making sounds in my sleep. That was really apparent to her and also to my colleague, James West, who came down to shoot video. I was really aware that I could not really ever relax. I would try to decompress when I got off, but there was never enough time to do that. I noticed myself start drinking more. The kind of things that is really common for guards, in general. I noticed myself sometimes wishing that somebody would spark a fight with me so I could just get out some of that pent-up aggression.

Sapien: What is the key takeaway that you want people to take away from reading this?

Bauer: My experience at Winn, in so many ways, made clear how conditions were affected by the profit motive of this private prison company. They basically have to deal with this contradiction where they are required to provide care and safety, security to prisoners, but they also are obligated to turn a profit. Their stocks are traded on Wall Street. There is always going to be a tension there. One of the main ways that CCA saves money is in staffing. Sixty percent of the cost of running their prisons is in staffing, so they pay much lower than the state paid its guards. They also didn't fill their positions, even to the bare minimum of what the contract required. That has a serious impact. I saw the ways that impacted conditions in the prison in terms of safety, in terms of medical care, in terms of mental health care. Also, safety of the surrounding community. Somebody escaped while I was there. There's 131,000 people in private prisons right now in the United States, so this is not an issue that's limited to this one prison.

Listen to this podcast on iTunes, SoundCloud or Stitcher For more, read Bauer's piece "My Four Months as a Private Prison Guard."