Sgt. Andrew Tahmooressi attended a nine-hour hearing Wednesday at a courthouse in Tijuana where he pleaded not guilty to weapons charges that were brought against him in April.

Despite some of his supporters' hopes that the judge would release the Marine reservist following the hearing, Tahmooressi was sent back to El Hongo Prison near Tecate to await a second hearing set for Aug. 4, The Los Angeles Times reported.

Tahmooressi's mother, Jill Tahmooressi, got to speak to her son Wednesday and thanked Judge Victor Octavio Luna Escobedo for allowing her to do so. Jill also said she was confident that her son would eventually be released.

"He's strong, he's confident," Jill told reporters.

For the first time since his arrest on April 1, Tahmooressi on Wednesday was able to give the judge his account of the events that night. Judge Escobedo also heard testimony from Mexican customs officials regarding Tahmooressi's arrest.

According to The Times, Tahmooressi was arrested in San Ysidro for crossing the Mexico-U.S. border with a pistol, rifle, shotgun and hundreds of rounds of ammunition in his pickup truck.

Tahmooressi told reporters following his arrest that he had recently moved to San Diego where he would receive post-traumatic stress disorder treatment at the Veterans Affairs hospital in La Jolla.

He said he had gotten lost while driving near the border and missed the turnoff to stay stateside. Tahmooressi also said he had never been to Mexico before but Mexican officials insisted that Tahmooressi wasn't telling the truth.

A hearing for last month was cancelled because Tahmooressi fired his previous attorney that was provided for him. His current attorney, Fernando Benitez, said the case is focused on the Mexican officials' procedural violations during Tahmooressi's arrest. He added that official paperwork seems to be missing.

Benitez said if Tahmooressi is convicted, he could face up to 10 years in prison. He also warned Tahmooressi and his mother, Jill, that the case go on for a few months over the course of several hearings, The Times reported.

More than 70 U.S. Congressional members have insisted that President Barack Obama's administration get involved in the Tahmooressi case. Earlier this week, two members wrote a letter to Judge Escobedo urging him not to punish Tahmooressi for making a "simple mistake at the border."

However, Mexican officials have argued that a "simple mistake" is not an excuse to break the law and also noted that there are several signs posted at the border warning visitors that it is a crime to bring firearms into the country.