Story highlights Marine says he was hit, left naked, shackled, deprived in Mexican prison

He says conditions have improved after media coverage

Over 100,000 people sign White House petition to demand his release

The U.S. Marine says he accidentally crossed Mexican border with 3 guns in March

Punched. Slapped. Cursed at. Deprived of water and food. Shackled to a bed with a "four-point restraint for almost a month."

U.S. Marine Sgt. Andrew Tahmooressi says that's what life was like for him in his first weeks in a Mexican prison. He ended up there after unwittingly crossing the border from California two months ago with several guns in his car -- firearms he says legally owns, but that it's unlawful to bring into Mexico.

Tahmooressi told CNN on Friday that things have gotten better for him. He gets by on phone calls to his family, his faith, reading, exercise, sleep and -- perhaps above all -- hope.

"I think that they will see that I'm not guilty of the crime they've (accused) me of doing," he said. "They'll just let me go."

Yet there's no guarantee that will happen.

JUST WATCHED Mom fights for release of son from Mexico Replay More Videos ... MUST WATCH Mom fights for release of son from Mexico 04:38

After a judge started and then quickly suspended a hearing Wednesday after Tahmooressi fired his attorneys, a Mexican judicial source said his next court hearing will be June 4 . But his mother, Jill Tahmooressi, said the next hearing is still weeks away, as it will take time for the new attorney to be briefed.

Until then, at least, Tahmooressi's days are going "by pretty slow."

But at least he's not being -- as he puts it -- "abused" any more, something he credits in part to the attention his case has gotten in the media and among politicians.

"Since I got media coverage, and people I guess realized that I'm not dangerous," Tahmooressi said, "it's been pretty relaxed and not so bad -- after the first month."

Prison authorities denied the abuse allegations and said he is being treated well.

'I got here accidentally; please let me turn around'

It was March 31. Tahmooressi had walked across the border into Tijuana to patronize an establishment popular with Marines from Camp Pendleton, his mother ,Jill, said.

As Tahmooressi explained, out of a parking lot, "I just made one wrong turn, and then that one wrong turn that I thought was going to take me north to San Diego was actually an on-ramp that swooped around back to the south and to Mexico."

At one point, he got "funneled" across the border.

"There was no way out of that except for if I had turned my truck around and drove into oncoming traffic," Tahmooressi said. "That would have been the only way that I could have done it."

According to Jill Tahmooressi, her son immediately disclosed to the border guards that he had weapons and requested that he be allowed to turn around, she said.

"The first thing he said to the first person that stopped him was, 'I got here accidentally; please let me turn around. I have three guns in my truck,' " his mother said.

A 911 tape released by U.S. Rep. Duncan Hunter, R-California, appears to support his version of events.

In it, the Marine is heard saying, "I crossed the border by accident, and I have three guns in my truck, and they're trying to take my guns from me."

After learning he's in Mexico, the 911 dispatcher responds: "There's nothing I can help you with then, sir. I do apologize. You're not on American soil anymore."

Tahmooressi asks whether 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."

Friend: Marine already suffers from PTSD

What happened, at a state penitentiary called La Mesa, left his mother "mortified."

In addition to being punched in the stomach and slapped in the face, Andrew Tahmooressi said he was at times "naked ... overnight in the cold" and "shackled in a way that made me want to stand overnight."

He added: "I was not allowed to drink water for about maybe 12 hours, and I was not given food for a certain amount of time like half a day or so."

While CNN could not independently verify these claims with Mexican authorities, if true, they would be the latest ordeal for a man who a close friend says was having trouble with post-traumatic stress disorder even before he was detained in Mexico.

"His PTSD started from combat. Now, he's got a whole other load of PTSD that he is going to get when he gets out of jail," said Sam Vranicar, who served with Tahmooressi in Afghanistan in 2010.

Tahmooressi has been able to speak with his friend when he calls Vranicar's house collect from the Mexican jail. The two have talked about 10 times, Vranicar said.

Vranicar said he's astonished that a Marine -- or anyone -- could be treated the way his friend describes.

"Being tied to a bed in four-point restraints and joint manipulation restraints -- like ways that a POW would be treated ... it's just ridiculous," Vranicar said. "I don't think it's right for any American to be in a Mexican jail treated like that. They are our neighboring ally, and it's inhumane."

'A different guy'

Vranicar had urged Tahmooressi to move from Florida to San Diego so that he could help him seek treatment for PTSD.

"As soon as he got out here, I realized that the Andrew that I used to know has gone," Vranicar said. "He became a different guy."

Vranicar and his wife noticed his friend was acting distant.

"I took him to La Jolla, he got diagnosed and he started seeing people on a regular basis," Vranicar said.

Not long afterward, he said, Tahmooressi made the wrong turn at an exit close to the Mexican border.

He had all his belongings, including his guns, with him, Vranicar said.

"It wasn't just his guns that he crossed with," he said. "It was everything he had. All his worldly possessions."

His mother said Tahmooressi was searching for permanent housing and often stayed in San Diego hotels.

Over 100,000 sign White House petition

Jill Tahmooressi said no one from the State Department in Washington had contacted her, but she heard from Bill Whitaker, chief of American citizens services at the U.S. Consulate General in Tijuana.

"I immediately let Mr. Whitaker know that Andrew was abused at the hands of the guards," she said.

U.S. Secretary of State John Kerry told CNN on Wednesday that he spoke with Mexican authorities about the veteran's case last week.

Tahmooressi and his family have pressed their case in other ways as well. That includes a White House petition his mother started on May 1 that, as of Friday night, had 110,000 signatures -- above the mark needed to garner an official government response.

The Marine has tried to appeal to U.S. lawmakers like Hunter, one of several who have petitioned for his release.

"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," 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."

And many more people not in positions of power have heard his story as well. He's grateful for all of the attention, which he believes has already contributed to his improved condition.

"I just want to say thank you to everyone who has been a part of this and has been helping me and rallying with me and signing my petition," Tahmooressi told CNN. "I can't thank you enough. I thank God for you guys."