(CBS News)the story of a former U.S. Marine, Jon Hammar, arrested in Mexico after bringing an antique shotgun across the border.
His parents told a harrowing story of abuse and violence by drug gangs inside that prison.
Now he is free, and for the first time, he's speaking for himself. CBS News spoke with the 27-year-old Monday.
Hammar returned home to Florida two weeks ago -- after spending more than four months in solitary confinement in a Mexican prison. His case is a sensitive topic for the diplomats who helped negotiate his release -- and a source of controversy among lawmakers who claim he was unjustly imprisoned.
In his first interview since his release, Hammar shared some painful memories.
Last August, Hammer and a friend decided to drive from Florida through Central America. Hammar told CBS News, "We wanted to experience the whole, you know, migration from Mexico -- to Panama, really."
Hammar, who had just completed three tours of duty in Afghanistan and Iraq, had recently been diagnosed with post-traumatic stress disorder. He planned on camping and surfing, a key part of his recovery. He said, "I can leave everything, all my problems on land and kind of go out on the water and enjoy myself."
Hammar also packed his great-grandfather's shotgun. He says it was a standard part of his camping equipment. "It's a .410 bolt action shotgun," he said. "You know, it's for hunting small birds."
He declared the weapon at the U.S.-Mexico border and bought a gun permit from a U.S. Customs agent. But when he crossed the border, Mexican officials detained him. Transporting a firearm or even a single round of ammunition is a federal crime in Mexico.
Asked why he thinks he was arrested, Hammar said, "Well, because I had a shotgun with me. And I don't think that the rules are as clear to, not only me, but to everyone else in Mexico. And I think it was really a big misunderstanding on everyone's part."
After four days in a holding cell, he was transferred to one of the country's largest prisons, and his family began receiving threatening phone calls. Hammar said, "There were threats made to me and my family. And the American consulate got involved and told the jail, you know, 'You can't -- we can't have this'."
Hammar refuses to reveal the identities of the individuals who made those threats, but his mother Olivia Hammar told CBS News that she believes her son was being beaten by inmates who are members of a powerful drug cartel.
Olivia Hammar said in December, 2012, "When he was initially put into the general population, we started receiving calls from members of the cartel that were saying, you know, 'We have your son and we're going to kill him'."
Those inmates threated to hurt and even behead her son unless she paid them thousands of dollars. After Hammar's mother reported the calls to U.S. officials, the threats stopped. At that point, Hammar was removed from the general population and placed in solitary confinement.
The room he was confined in was "basically like an electrical room, kind of like a garage," Hammar said. "There were three walls, a ceiling, and a floor," he added. "It's normally where the guards would keep like, their book bag or something ... in the corner of the room. They put a bunk in the corner and put me in the corner in the back of this room."
Hammar said he was chained to the bed by his foot. Hammar said some days he wasn't given food. He doesn't speak Spanish, so he rarely spoke to guards. He made occasional calls to his parents and received infrequent visits from U.S. Consulate officials.
He remained behind bars for more than four months. Mexican officials dropped the case days before Christmas without an explanation. Hammar's family credits the press and U.S. lawmakers for pressuring Mexican authorities.
Hammar said of the ordeal, "Some people get thrown fastballs and you get dealt a hand in life. And you have to play with that hand."
Asked if this was a fastball, Hammar replied, "Yeah, it happened pretty fast."
Hammar says he takes responsibility for his actions. He's a quiet guy, very reluctant to talk about himself, but he wanted to share his story because his family believes that the public attention was responsible for pressuring Mexican authorities into releasing him.
Hammar had health issues right after he was released. He was hospitalized for five days because of stomach issues, lung infections. But he's recovering. He says he's trying to work out and get healthy.
Mexican authorities dropped the case. However, it sounds like there may be future litigation. Hammar said Customs authorities on the U.S. side told him what he was doing was legal. That paperwork hasn't been recovered. So it's unclear whether that case can be made.
Hammar wants to urge other veterans to seek therapy for PTSD. For more information on The Pathway Home, a non-profit program that veterans attend for free to receive PTSD treatment go to their website here.
For Margaret Brennan's full report, watch the video in the player above.