Marine sergeant jailed in Mexico on gun charges speaks exclusively 'On The Record'

The U.S. Marine who mistakenly crossed into Mexico with guns registered in the U.S. told Fox News Channel's Greta Van Susteren that authorities south of the border showed no interest in hearing his story before they locked him up two months ago.

In an exclusive interview from a federal prison in Tecate, Sgt. Andrew Tahmooressi, who served two tours of duty in Afghanistan, told the "On the Record" host he tried to explain that he had taken a wrong turn and was unable to avoid crossing at the San Ysidro checkpoint on the night of March 31.

"[A Mexican border guard] got on the walkie-talkie and was communicating what was going on," Tahmooressi said. "I think what he said was, 'Hey we've got a guy down here with three guns.'"

That message brought a Mexican Marine to the scene.

"He just took control," Tahmooressi said of the officer. "He didn't seem to care at all about anything that I had to say. It was like a math equation in his head. Three guns, man equals prison."

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    Tahmooressi, a Florida native who had been living in California while seeking treatment for Post-Traumatic Stress Disorder, spoke to Fox News hours after his first court appearance before a federal judge in Tijuana. Prior to the hearing, Tahmooressi fired his attorney, who had previously told him in an email obtained by to lie to authorities and claim he had never been to Tijuana.

    Since his arrest, Tahmooressi has faced death and rape threats, has had his feet and hands shackled and lost weight, according to his mother, Jill Tahmooressi. She has been able to visit him and speaks with her son by phone several times a week.

    When Tahmooressi realized that he was entering Mexico with the weapons at the poorly-marked crossing at the San Ysidro checkpoint, Tahmooressi immediately called 911, but was told by American officials that since he was in Mexico there was nothing they could do to help him.

    Mexican authorities have accused Tahmooressi of changing his story, possibly over whether he had ever been to Tijuana. By his own admission, Tahmooressi acknowledged at the border he had registered weapons and that he had no intention of even entering Mexico. That should have allowed him to turn around, according to U.S. border officials, who told Fox News the entire ordeal could have been stopped with a little discretion and a phone call or two.

    Tahmooressi, who fellow Marines described as selfless and disciplined, appears to be in a better frame of mind in recent days, according to his mother. Wednesday's hearing was the first of several, with subsequent proceedings to involve hearing the 911 tape and bringing court officials to the border crossing.

    A State Department spokeswoman said Secretary of State John Kerry raised the issue with Mexican officials, but the Obama administration has said little publicly about the case.

    Watch the full interview with Sgt. Andrew Tahmooressi on 'On The Record with Greta Van Susteren" Thursday at 7 p.m. Eastern on Fox News Channel.