By Ashley Fantz, Nick Valencia and Nick Parker
(CNN) -- A judge has scheduled a new hearing for a U.S. Marine and Afghanistan war veteran who's been held in a Mexican prison for nearly two months.
Sgt. Andrew Tahmooressi's next day in court is scheduled for June 4, a Mexican government judicial source told CNN.
The judge started and then quickly suspended a hearing Wednesday after Tahmooressi fired his attorneys, the source said.
Tahmooressi is accused of illegally entering Mexico with three weapons. His family maintains that he legally owned the weapons and accidentally crossed the border.
It is illegal to bring guns into Mexico.
Mother Jill Tahmooressi told CNN Wednesday that her son had made an innocent mistake.
"He is relieved that he'll be able to go before the judge and explain precisely how he made that accidental wrong turn and ended up in the dilemma that he's in right now," she said.
The case has draw attention from several U.S. lawmakers and U.S. Secretary of State John Kerry, who told CNN Wednesday that he spoke with Mexican authorities about it last week.
"We are working on determining whether or not certain evidence that has been presented is meeting the standard that's necessary to be able to hold that young Marine, and we're trying to find out exactly what the fact pattern is, but we are working on that," he told Chris Cuomo on CNN's "New Day."
911 call: 'I crossed the border by accident'
"I'm at the border of Mexico right now. And my problem is, I, I crossed the border by accident and I have three guns in my truck and they're trying to take my guns from me," the Marine told a 911 dispatcher in March.
In a recording of the call released by U.S. Rep. Duncan Hunter, R-California, the Marine appears unsure of whether he crossed the border and exasperated that Mexican authorities are trying to take his weapons.
"There's nothing I can help you with then, sir," the 911 dispatcher says after learning he's in Mexico. "I do apologize. You're not on American soil anymore."
Tahmooressi asks if authorities have a right to take his guns.
The dispatcher tells him he should have seen large warning signs on the freeway saying it's illegal to enter Mexico with guns.
"There are warning signs that do say that as you're driving down the freeway, before you enter Mexico," she says.
"Yeah, I was hoping there would be a turnaround point," he says, "but there never was."
Mom: Marine had been preparing to start fresh
The Marine's mom said he accidentally crossed into Mexico with three personal firearms -- all bought legally in the U.S.
The 25-year-old had intended to drive to meet friends in San Ysidro, California, on March 31.
He was moving from Florida to California in the hope of getting a job and continuing treatment he had just begun for post traumatic stress related to his two combat tours, she said.
With all his possessions in his truck, Tahmooressi accidentally drove across the border, she said.
When he realized his mistake, his mother said, he dialed 911 and asked the operator to help him. No help came, Jill Tahmooressi said. Her son first encountered Mexican customs agents, she said, and he believed they understood that he'd made an innocent error. They seemed to be getting an escort car to help him, she said.
But officers with the Mexican military interfered, she told "New Day," and her son was arrested.
Now he's in isolation -- being held away from the general population in a Mexican federal prison -- and is constantly watched by a guard, she said.
Letter to lawmakers
The Marine has tried to appeal to U.S. lawmakers.
"I accidentally drove into Mexico with 3 guns ... a rifle (AR-15), a .45 cal pistol and a 12 gauge pump shotgun with no intensions (sic) on being in Mexico or being involved in any criminal activities," Andrew Tahmooressi wrote in a statement of innocence to Hunter, who sits on the House Armed Services Committee.
"I have rights to all 3 weapons," he wrote. "They are under my name. ... Please help me."
Hunter is among several lawmakers who have petitioned for Tahmooressi's release.
"Mexico's Attorney General is in a position to deal with Andrew's case and ensure its quick resolution. ... It is necessary that the AG intervene and expedite proceedings at the very least. And so far there's been no validation from Mexico that Andrew didn't make a directional mistake at the border," Hunter said in a statement this month.
CNN's Rosalina Nieves and Rafael Romo contributed to this report.
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