Tahmooressi, 25, was arrested March 31 after he said he mistakenly took three guns across the border into Mexico. He said 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.
"I'm not a guilty man, and you can probably hear it from my voice and the sincerity in my voice," he said. "I'm innocent, and it was just a big mistake."
Speaking from his jail cell in El Hongo Penitentiary in Tecate, Mexico, Tahmooressi told CNN he's feeling more optimistic about his chances for release.
"I'm not as down as I once was," he said. "My relationship with the guards has turned more into a friendship, so I don't feel as alone, I guess. Once the media started covering it ... things did start changing. ... I'm just trying to keep my cool and stay relaxed."
"I feel like the punishment was never necessary from the beginning. But once the (Mexican) military people got involved, they were like, 'Look what we found, we found these guns, good for us. Let's get this guy incriminated.' There was some good people at the border who were going to do the right thing, and that's how it should have been from the start," he said.
Tahmooressi is next scheduled to appear in court Wednesday.