Zac, a participant in the A&E show "60 Days In." Screenshot/A&E

It's all too common for veterans in the US to wind up in jail.

And behind bars, many of them don't have access to the services they need to get their lives back on track.

That's what the participants on the A&E documentary series "60 Days In" learned during their stay at Clark County Jail in southern Indiana.

The show follows seven people who go undercover as inmates for two months to expose problems within the system.

One of the participants, Zac, estimated that 10% of the inmates he lived with were veterans, all of whom suffered from depression or post-traumatic stress disorder. Like many drug-addicted inmates, they often resorted to homemade drugs to self-medicate.

He said that most inmates weren't aware the jail offered veterans advocacy services and an Alcoholics Anonymous support group — and that jail employees rarely advertised the fact that such programs existed.

"Regardless of whether or not they're in jail, they still took the same oath that they would protect the country with their life," Zac told Business Insider. "They still deserve to be treated for issues they developed because of that oath they took."

Veterans in jail are more likely to suffer from mental-health issues than other inmates, according to the most recent data from the Bureau of Justice Statistics. Veterans are much more likely than civilians to commit suicide.

Zac himself is a veteran, having served as a combat engineer with the Marines in Afghanistan.

When he returned home from deployment in 2010, he said, he refused to talk about his experience with friends and family. For a few months he found comfort in alcohol, consuming more than $1,500 worth a month.

Zac, right, with Brian, a Clark County Jail inmate and fellow Marine. Screenshot/A&E Zac now advocates 22Kill, a group that raises awareness of veteran suicide.

Though Zac assumed a false identity for the show, he did incorporate details from his military background into his cover story.

"It definitely gave me a degree of respect," he told Business Insider. "Their first thought was probably, 'This guy probably knows how to fight.' It helped keep me out of some situations."

For part of his stay at Clark County Jail, Zac shared a cell with two other Marines. In one scene from the show, when Zac accidentally sleeps in and misses breakfast, his cellmate offers him half of his meal, an almost unheard-of act of kindness in jail.

"There was a level of camaraderie — we watched out for each other," Zac said. "The saying goes, 'Once a Marine, always a Marine.' We were in different theaters, different wars, but they're still Marines, and you watch out for them the same way you would anywhere else."

The 11th episode of "60 Days In" airs Thursday at 10 p.m. ET.

Watch a clip from "60 Days In" below:

Update: Clark County Sheriff Jamey Noel has provided Business Insider with the following statement:

When a person is booked into the Clark County Jail during the initial processing questioning it is asked of that person to identify if they are currently or if they have served in the United States Military.

Once a person has been identified as a veteran or member of the United States Military that information will be forwarded to the Veterans Justice Outreach Coordinator. The Veterans Justice Outreach Coordinator is also provided with a list of all person who is processed into the Clark County Jail which allows them access to cross reference their data base to indent ify anyone who might have not provided the information at the time of processing.

Once a person is identified as a veteran or Member of the United States Military the Veterans Justice Outreach Coordinator makes contact with those persons while incarcerated and provides them with information on how to obtain veterans services such as, disability benefits, medical and mental health assistance and works with them hand in hand throughout the court process.

The Veterans Justice Outreach Coordinator has recently started the process to implement a monthly group style meeting that will allow all veterans incarcerated to meet. The meeting will allow the veterans to ask questions and seek assistance while they are incarcerated as well as assist them in the transition back into society upon their release.