ATLANTA, Sept. 20 (UPI) -- Sgt. Andrew Tahmooressi, a U.S. Marine reservist currently jailed in Mexico," is "highly despondent," his mother said.

The 25-year-old was arrested in March after he said he mistakenly took three guns across the border into Mexico.


He's still sitting in the El Hongo Penitentiary in Tecate, Mexico, and his mother, Jill Tahmooressi, told CNN her son's mental state is deteriorating.

"He is lacking confidence that this will end soon and expeditiously," she said. "All we have ever asked for is an expeditious due process since he is a current Marine under contract until 2016. And the merits of the case surely point to accidental entry."

Jill Tahmooressi said her son's communication with the outside world has been limited in the last week or so after the prison phone broke.

"He has unresolved, or untreated PTSD, and he cannot get the cognitive therapy behavior that veterans of America receive ... in a Mexico jail, where there is no such thing," she added. "He's highly discouraged there is no light at the end of the tunnel."

Tahmooressi maintains his innocence, saying he had no intention of crossing the border and was originally told he could turn around to return to the United States before he was arrested.

Alejandro Gonzalez Guilbot, the director of the Tijuana checkpoint where Tahmooressi was detained, said the Marine had a chance to surrender his weapons and return to the United States.

"Never, and I want to say this categorically, never did he say that he had made a mistake," Gonzalez said. "He never said, 'I got lost.' He never said, 'I am a Marine.' "

The U.S. State Department refused to comment on whether it believes Tahmooressi's explanation of events.

"We continue to provide extensive consular assistance to Mr. Tahmooressi, and will do so until his case is resolved," the department said in a release. "Consular officers have visited Mr. Tahmooressi 20 times since his arrest on March 31. While we won't go into detail about our private diplomatic discussions on this case, U.S. officials, including the Secretary, have talked to Mexican officials at the highest levels regarding Mr. Tahmooressi's case."

Tahmooressi faces up to 21 years in prison. His next court date is Sept. 29