Parents plead for release of former US Marine held in Mexico jail By Justin Finch, NBCMiami.com Jon Hammar's Marine veteran son is being held in a Mexican prison - and he's desperate to bring him home safe. "I don't know what to do to get him out before he gets killed," he said. The holidays have been unbearable for the Hammar family in Palmetto Bay - hoping each day that they'll soon see their son Johnny again. They last saw him back in August, before he took off in a Winnebago with a friend for a road trip to Costa Rica, where the two planned to surf. "I actually thought it would be a good idea for him to go to Costa Rica, but I wanted him to fly," Olivia Hammar said. A getaway is just what the 27-year-old Hammar needed. His service as a Marine includes stints in Afghanistan - where he worked a security detail for President Hamid Karzai -and patrols in Iraq. Hammar's family says he was deeply hurt by the loss of his close friend, Marine Cpl. Albert Gettings, in combat in Iraq's Fallujah section. Grieving Daughter Asks for Public's Help Days after Hammar left for Costa Rica, they learned he was being held in Mexico's Matamoros prison - charged with carrying an illegal weapon. Even worse, they heard he was in the clutches of the Zetas, a dangerous drug gang. The Hammars say they were haunted by late-night phone calls. The father described one. "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," he recounted. Said his wife, "At some point the phone calls stopped, so we assumed that he had been isolated. But you didn't know whether he had been isolated or he had been killed. For months, the Hammars have been trying to get their son home through Mexico's courts. But in recent weeks, they say their son has been pressured to plead guilty to the gun charge, which could land him 15 years behind bars. The Hammars have also reached out to Washington, but have hit walls along the way. "The response from everyone is Mexico is a sovereign nation, and, you know, we can't force them to do anything, which we know, but this is an outrage," Olivia Hammar said. An online petition is gathering signatures to try and help bring Johnny Hammar home. Click here for more information.