In a must-see interview, ‘On The Record’ traveled to Mexico to talk to the mother of jailed Marine Andrew Tahmooressi. The 25-year-old has been held in a Mexican prison since April 1, when he took a wrong turn in San Diego and reached the border.

When Mexican border guards searched his car, they found three guns that he had legally purchased in the United States. Instead of having him turn around and go back, he was locked up.

Since then, his mother Jill Tahmooressi has been calling on lawmakers and the State Department to intervene. In the sneak peek above, Greta Van Susteren asked Jill about her son’s state of mind.

“He’s cautiously optimistic,” Jill said, “because he’s in a foreign country. It’s a foreign prison; it’s a foreign legal system. We still don’t understand our rights; we don’t understand our legal representation.”

Hear more in the clip above and tune in to On The Record tonight at 7p ET on Fox News Channel for the full interview.