Parents: US Marine detained in Mexico for bringing shotgun across border Carolyn Kaster / AP file President Barack Obama, accompanied by House Speaker John Boehner of Ohio, speaks to reporters in the Roosevelt Room of the White House in Washington, Friday, Nov. 16, 2012, as he hosted a meeting of the bipartisan, bicameral leadership of Congress to discuss the deficit and economy. AP Photo/Carolyn Kaster The parents of a former U.S. Marine jailed in a violent corner of northern Mexico said Monday that her son was losing hope after being arrested in August for possessing a shotgun that was a family heirloom. Handout / Reuters file Jon Hammar, a former U.S. Marine jailed in northern Mexico is pictured here in an undated photograph provided by his family. Hammar was driving to Costa Rica on a surfing expedition when he was arrested for "possession of a deadly weapon" because of the length of the barrel of his shotgun, his parents say. "I don't know what to do to get him out before he gets killed," father Jon Hammar Sr. told NBC Miami. Jon Hammar Jr., 27, was heading to Costa Rica to go surfing when he crossed into Matamoros, Mexico, from Brownsville, Texas, in a beat-up old Winnebago motor home he and a friend bought especially for the trip. With him was a family heirloom -- a shotgun. He had registered the shotgun with U.S. Customs and Border Protection officials on the U.S. side of the border, declaring he planned to take it with him into Mexico. Read more about this story at NBCMiami.com Despite being told that the shotgun, a Sear & Roebuck model that once belonged to his great-grandfather, posed no problem Hammar was arrested as soon as he crossed into Mexico. The arrest came when he tried to register the gun with Mexican customs officials, his parents and their Mexican attorney told Reuters. "The crux of it is the length of the barrel," said his mother, Olivia Hammar, 46, of Palmetto Bay, Fla. "There's an old law on the books that says it can't be under 25 inches," she said. It's a 2-foot barrel and it can't be under 25 inches ... . It's strictly a technicality. The U.S. Embassy in Mexico City said Hammar was charged with possession of a deadly weapon. And the family lawyer, Eddie Varon-Levy, said Hammar faces up to 12 years in prison if he is found guilty. Making matters worse, Hammar suffers from post-traumatic stress disorder from the death of a fellow Marine who was killed by a sniper's bullet when the two served together in Fallujah, Iraq. He had just completed treatment for PTSD at a center for veterans in California last year. His ordeal there, in one of the most violent corners of Mexico, has included being shackled to a bed and receiving death threats and extortion demands from drug cartel gangsters who run the prison known as CEDES in Matamoros like their personal fiefdom, Hammar's parents say. "He's getting more and more hopeless," said Olivia Hammar, the publisher of an architecture and interior design magazine. Hammer's parents, too, are increasingly concerned. They heard their son is in the clutches of the Zetas, a dangerous drug gang. The Hammars say they were haunted by late-night calls demanding that $1,400 be wired through Western Union to ensure their son's safety. Jon Hammar Sr. recounted one call: "You know, one o' clock in the morning, we have your son and this doesn't have anything to do with the police, we're gonna kill him if you don't send us money." After that call, Hammar was isolated from the general population of the prison, at the request of U.S. Consular officials. "This is just an outrageous case," said Representative Ileana Ros-Lehtinen, a Republican from Florida who chairs the House Foreign Affairs Committee and considers Hammar "a hero" because of his combat duty. "If the parents had not told me about it, and his friends had not gotten involved, I would say that it was just not possible for someone to be in so much trouble for doing the right thing," Ros-Lehtinen said. She added Hammar had been "denied his most fundamental rights" in Mexico and urged the State Department to take a much more active role in his case. NBC Miami and Reuters contributed reporting.