The documentary series "60 Days In" followed nine law-abiding citizens who went undercover as inmates in an Atlanta jail for two months.

The undercover inmates were exposed to drugs, violence, and frequent confrontations with jail staff.

Consequently, a participant who had worked as a police officer ended up leaving the force after the show ended, because he couldn't stand to send people to jail.

Filming of the show ended prematurely when one of the participants blew her cover story.

A police officer from Texas named Alan spent eight weeks undercover in a jail as part of "60 Days In," the A&E documentary series that sent nine law-abiding citizens to go undercover at Atlanta's Fulton County Jail.

And when he got out, he said, he quit the force and became a car salesman.

"I couldn't go to bed at night knowing that if I stopped somebody with a little dime bag of weed, I were to arrest them and put them in a place like that — I wouldn't be able to live with myself," he said.

Alan (the participants didn't use their last names) and the other inmates were given fake identities and booked under false charges for the show, and were tasked with learning the inner workings of inmate life and exposing secrets even the jail's staff didn't know about.

They were alarmed at the harsh reality of life in jail, and they had good reason to be.

Much of the show, which wrapped up its fourth season last week, focused on drug use within the jail, culminating with Alan discovering how illegal drugs such as meth make it into the jail.

He learned that when there's demand for certain drugs, inmates will coordinate with accomplices on the outside, who then get arrested on purpose and smuggle the drugs into the jail. Once the drugs are inside the facility, they're distributed among each section of the jail by trustees, inmates who are selected for tasks like passing out meals.

"These guys were coming in with things in their body cavities that we just weren’t checking," chief jailer Mark Adger said. After Adger debriefed with the undercover inmates, he said he began instructing his staff to do more thorough inspections of new inmates when they first arrive.

Much of the drug trade was controlled by gangs — 20% of the jail population has affiliations with organized gangs, according to statistics provided by Adger. The undercover inmates quickly learned that each section of the jail has a strict social hierarchy, with the "pod boss" typically being the most senior gang member. Even inmates unaffiliated with gangs were under the constant threat of violence, an undercover inmate named Nate told Business Insider, as fights were a common strategy for lower-ranking inmates to climb the ladder.

Stephanie, one of the undercover inmates, complains about a gas leak in the women's pod. A&E The show also highlighted the adversarial relationship between inmates and jail staff, who were not made aware of the presence of the undercover inmates. One of the participants, a public health analyst named Emmanuel, got into a shouting match with a corrections officer who was reluctant to help after Emmanuel complained there was blood and mucus on his cell wall left by a previous inmate.

"It's a common pattern with the COs that it takes challenging, just being belligerent, in order for them to give you respect," Emmanuel said on the show. "It's sad. They'll respond to you cursing at them, you yelling at them, and honestly, that doesn't help the inmates that are in here when they go out, because they know they can just get something by just yelling."

In other scenes, corrections officers were seen ignoring requests for basic amenities and waiting more than an hour to act after inmates in the women's section of the jail complained of a gas leak. Adger said jail staff are constantly wary of inmates trying to "play" them by distracting them from monitoring illegal activity in the cells, although he didn't excuse their behavior.

"They see so many people and they become desensitized. We have to re-sensitize them to some degree," he told Business Insider.

Unfortunately for Adger, filming of "60 Days In" went off the rails when one of the participants deliberately blew her cover to another inmate she had formed a relationship with, forcing him to shut down the undercover program about two weeks early. The last episode of the season followed Adger as he attempted to safely withdraw the participants before word spread to inmates that there were undercover agents in the jail.

You can read Business Insider's coverage of "60 Days In" here.