The attorney for the Marine being held in a Mexican prison on gun charges told Fox News’ Greta Van Susteren Thursday that the case is “tainted by several human rights violations.”

A Mexican federal judge sent Sgt. Andrew Tahmooressi back to prison Wednesday after he made his first official courtroom appearance since being locked up more than three months ago for accidentally crossing the border with guns in his pickup truck.

Fernando Benitez, Tahmooressi’s lawyer, told Fox News Thursday he believes the entire case against his client has been tainted because of the way it was handled by Mexican authorities, and should be dismissed.

“Right now we have a lot of evidence that the arrest is tainted by several serious human rights violations,” Benitez said on “On the Record with Greta Van Susteren.” “The further we go into evidence, into that topic, the more clear it will become I believe.”

Benitez said the violations occurred during the time Tahmooressi was held at the customs point of entry, but said he was not at liberty to discuss them in detail.

Benitez said Tahmooressi was candid during his testimony at the hearing and was in good spirits.

“He started off pretty upbeat,” he said. “He was straightforward; he talked at length and in detail about everything happened on the 31 of March.”

Tahmooressi has been held since March 31, when he accidentally drove into Mexico at the San Ysidro, Calif., Port of Entry late March 31, after becoming disoriented from poorly lit street signs and being in a position on the road unable to make a last ditch U-turn. His family believes his post-traumatic stress disorder also may have contributed to his confusion.

He was charged with violating Mexico's strict gun laws because he had three registered guns, along with all his worldly possessions, in his vehicle.

Benitez said he is hopeful that the judge will rule in Tahmooressi’s favor.

“I believe his story and I believe the judge will believe it too with more evidence,” he said.