Marine veteran Ian Mcdonough was the only person with fellow Marine Jon Hammar when they were both detained August 15 by Mexican police at the U.S. border.

While Mcdonough was released three days later, 27-year-old Hammar was arrested on federal charges for possessing his grandfather's antique shotgun, a weapon reserved for military use in Mexico.

Now the Florida veteran, who served two tours of duty in Iraq and Afghanistan, faces a felony charge and up to 12 years in one of Mexico's most dangerous facilities, the Matamoros state prison. 

In an exclusive interview with Fox News Latino, McDonough details what happened the day they crossed the border. He says every indication from Mexican agents was that they would be fined and let go. He also says the U.S. Border Patrol should take some responsibility and he pleads with President Obama to act on freeing Hammar. 

McDonough feels guilty, he says, for leaving his best friend "in hell." And he's appalled by Mexico's decision to chain Hammar's ankle. 

"I went and served in Bukkah and Iraq and I didn't chain nobody to a bed," he said. "He hasn't shown to be dangerous. He hasn't attacked anybody. He hasn't verbally abused anybody. He hasn't tried to escape. He went to the police station without handcuffs on. He went with the trust that this was just a legal issue that needed to get resolved."

Both men met at a Pathway Home for PTSD Veterans a year ago and immediately became best friends. They were on their way to surf in Costa Rica as a jump start to a new life.

Hammar's parents came forward to the media on December 6 hoping the publicity will push Mexican authorities to act.

Since then, U.S. Senator Bill Nelson (D-Fla.) and Representative Illeana Ros-Lehtinen (R-Fla) have spoken on the House and Senate floors asking Mexican authorities to release Hammar.

The family lawyer, Eddie Varon-Levy, hopes the case can be resolved before Hammar's next court date on January 17.

Follow us on twitter.com/foxnewslatino
Like us at facebook.com/foxnewslatino

Bryan Llenas currently serves as a New York-based correspondent for Fox News Channel (FNC) and a reporter for Fox News Latino (FNL). Click here for more information on Bryan Llenas. Follow him on Twitter @BryanLlenas.

Follow us on twitter.com/foxnewslatino
Like us at facebook.com/foxnewslatino