(Fox News) The Marine sergeant arrested for carrying loaded rifles into Mexico contemplated suicide during a harrowing 214-day imprisonment that included beatings, chains and being stripped naked for hours at a time, he said Thursday during an exclusive interview with Fox News’ Greta Van Susteren.

“I was vulnerable, feeling very vulnerable,” Andrew Tahmooressi said of his initial days inside the La Mesa prison in Tijuana. “I know there are some messed up people in this world, and prison’s a good place to find them.”

Tahmooressi, a 26-year-old veteran of two tours in Afghanistan, was arrested on March 31 after mistakenly crossing the border with three registered guns. At one point, he tried escaping from La Mesa, only to be caught and beaten by guards.

“I was very afraid. I felt like it would be the last night of my life right there, that these guys were going to kill me,” he said. “I thought running away was my only hope to get away from a situation like that.”

“I’m going to be OK, everyone. I’ll be just fine, I promise you.”

– Marine Sgt. Andrew Tahmooressi

Although he said he got “pretty far,” he was unable to get through a gate, and was subsequently beaten and chained by guards. At one point, he was stripped naked and strapped to a bed for nearly nine hours.

Later, Tahmooressi, who faced the prospect of being jailed for 21 years, tried to kill himself by smashing a light bulb and stabbing himself in the neck, though guards discovered him and brought him to a prison hospital in time to save his life.

Tahmooressi eventually was moved to a safer prison in Tecate, where he remained until a Mexican judge ordered Tahmooressi freed on Friday on humanitarian grounds after he’d spent seven months behind bars. Tahmooressi, who had been living out of his pickup in the San Diego area while he sought treatment for post-traumatic stress disorder when he was arrested, returned to his family in Florida on Saturday.

Tahmooressi family spokesman Jonathan Franks said the judge acted on a recommendation from the PGR, the Mexican Attorney General’s Office. In that motion, the prosecutor “essentially withdrew the charges,” Franks said. Moments later, the trial judge issued an acquittal in Andrew’s case, calling for an “immediate and absolute release.”

Now home for good, Tahmooressi told Van Susteren he’s not sure he’ll keep his guns, and now wants to keep busy, finding a job and “doing productive things.”

But he says he’s grateful for the support he had through the ordeal from Americans across the country who were outraged at his jailing.

“I’m going to be OK, everyone,” he said. “I’ll be just fine, I promise you.”

Although Tahmooressi’s supporters have blasted President Obama for not doing more to get him freed, several politicians, including former New Mexico Gov. Bill Richardson, members of Congress Duncan Hunter, R-Calif.; Ileana Ros-Lehtinen, R-Fla.; Ed Royce, R-Calif.; and Matt Salmon, R-Ariz., were among those who worked to secure his release.

“The totality of diplomacy, the judicial process, the legal strategy and the importance of the American-Mexican relationship resulted in Andrew’s release,” Richardson said after the announcement. “And now we have this great outcome. Andrew’s coming home.”

Richardson told Fox News Tahmooressi is seeking privacy and still needs to receive treatment for his PTSD, something that wasn’t available in Mexican prison– a key argument put forth by defense attorney Fernando Benitez.

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