WNBA star Brittney Griner reflects on the “mistake” that led to her detention in Russia on the “20/20” special.

WNBA star Brittney Griner spoke for the first time about her harrowing months-long detention in Russia and the “mistake” that landed her nine years in prison on a special edition of ’20/20′ that aired tonight at 10 p.m. ET on ABC.

“I could just visualize everything I worked so hard for, just breaking down and leaving,” Griner told “GMA” co-anchor Robin Roberts.

Griner, 33, a two-time Olympic gold medalist and nine-time WNBA All-Star who plays for the Phoenix Mercury, was arrested on February 17, 2022 at Sheremetyevo International Airport in Khimki after being accused of having vape cartridges. containing cannabis oil, which is illegal in the country.

Recounting the “mental lapse” that led her to forget the cannabis oil cartridges in her luggage, Griner said she woke up late the morning she was sent to Russia to play in the offseason of the WNBA and that she had packed her bags while she was in “panic mode.”

“At that point, I just threw all my stuff in there, closed it and said, ‘OK, I’m ready,'” she told Roberts.

Griner, who reflects on the experience in “Coming Home,” a memoir to be released May 7, recalled the sinking feeling she felt when she realized she had forgotten two cartridges of cannabis oil in his luggage after security asked him to pass. her bag at the airport.

“I’m just like, ‘Oh, my God.’ Like, “How did I…how did I make this mistake?” “, Griner said.

“I could just visualize everything I worked so hard for, just breaking down and walking away.”

Griner was arrested and, after her trial was delayed for several months, she pleaded guilty to drug charges on July 7, 2022, claiming that the vape cartridges containing cannabis oil were unintentionally in her luggage . She said she had “no intention” of breaking Russian law and had packed the cartridges by accident.

“You know, there are those who say: ‘Come on. How did you know you had cartridges in your luggage?’ asked Roberts.

“It’s so easy to make a mental mistake,” Griner said.

“Certainly, my mental breakdown was on a larger scale. But that doesn’t take away from how it can happen,” she added.

The U.S. State Department classified Griner as “wrongfully detained” in May 2022, allowing additional resources to be allocated to her case as the Biden administration worked to secure her release.

Griner spoke of poor conditions in prison as she awaited trial, saying she didn’t always have toilet paper and the toothpaste she was given expired about 15 years ago.

“That toothpaste was expired,” she said. “We used to put it on black mold to kill mold on the walls.”

“The mattress had a huge blood stain on it, and they give you these two thin sheets,” she added. “So you basically lie on the bars.”

Griner was sentenced to nine years in prison on August 4, 2022, and a judge in October 2022 rejected an appeal filed by Griner’s lawyers.

After her conviction, Griner was transferred to a penal colony in Russia’s Mordovia region – a labor camp where her job was to cut fabric for Russian military uniforms.

“What were the conditions like there? » asked Roberts.

“Really cold,” Griner said. “It’s a labor camp. You go there to work… there is no rest.

Griner said the freezing temperatures took a toll on her health and led her to cut off her long dreadlocks.

“How does it feel to lose that part of you too?” » Roberts asked Griner.

“Honestly, this had to happen. We had spiders above my bed making nests,” she said.

“My dreads started to freeze,” she added. “They would just stay wet and cold and I would get sick. You have to do what you have to do to survive.

During her detention, Griner’s top athletes and family, including his wife Cherelle Griner, have been strong advocates for her release and have continually called on the Biden White House to intervene and bring her home.

Amid growing pressure on the White House to secure her freedom, Griner was released on December 8, 2022, after the United States agreed to exchange her for convicted Russian arms trafficker Viktor Bout.​​

“You said you felt like you were letting yourself, your family, your teams down…how did you overcome that? » asked Roberts.

“I don’t think I really made it until the end,” Griner said. “At the end of the day, it’s my fault. And I let everyone down.

Griner reflected on the moment she learned she was going to be released, saying, “I was so thrilled,” but added that she was disappointed that Paul Whelan — another American unjustly detained in Russia — had been left over.

“I was thinking…you’re seriously not going to let this man come home now?” Griner spoke about Whelan, who was convicted of espionage and sentenced to 16 years in a Russian prison.

Since her release, Griner has become a vocal advocate for Americans unjustly detained abroad.

In a heartfelt Instagram post on December 16, 2022, in which she thanked those who advocated for her release, Griner pledged to “do whatever I can to help” bring home other unjustly detained Americans abroad.

“President Biden, you brought me home and I know you are committed to bringing Paul Whelan and all Americans home too,” Griner wrote. “I will use my platform to do whatever I can to help you. I also encourage everyone who played a role in bringing me home to continue their efforts to bring all Americans home. Every family deserves to be whole.

ABC News’ Eboni Griffin, Joseph Diaz, Gail Deutsch, Susan Welsh, Netsanet Negussie, Kaitlin Amoroso, Danielle Genet and Chris Donovan contributed to this report.