Brittney Griner appears in Russian court as pressure mounts on Biden White House to secure her release

WNBA star Brittney Griner appeared in a Russian court on Thursday morning for the third day of her trial, as the Biden administration works to secure her release.

Griner did not testify but several Russian individuals testified as character witnesses about their experiences with the basketball star.

The first witness was Maxim Ryabkov, the director of UMMC -- the Russian basketball club in the city of Yekaterinburg for which Griner played in the WNBA offseason. The second witness was team doctor Anatoly Galabin, who said that she never tested positive for doping while playing for the team. And the third witness, Evgenia Belyakova, one of Griner's Russian teammates, said that Griner was the leader of the team.

Griner pleaded guilty on drug charges in a Russian court last week, saying that the vape cartridges containing hashish oil were in her luggage unintentionally.

Griner, who has been detained in Russia since Feb. 17, said she had no "intention" of breaking Russian law, and was in a rush but did not mean to leave the cartridges in her bag.

The WNBA star's trial, which is taking place in Khimki -- a suburb of Moscow -- began on July 1, more than 4 1/2 months after Griner was detained.

Griner, a two-time Olympic gold medalist, was visiting Russia to play basketball in the off-season when she was detained at Sheremetyevo International Airport after being accused of having vape cartridges containing hashish oil, which is illegal in the country.

Her legal team told ABC News in a statement last week that her "guilty" plea was informed by a discussion with her Russian attorneys.

"Brittney sets an example of being brave. She decided to take full responsibility for her actions as she knows that she is a role model for many people," they said in the statement. "Considering the nature of her case, the insignificant amount of the substance and BG's personality and history of positive contributions to global and Russian sport, the defense hopes that the plea will be considered by the court as a mitigating factor and there will be no severe sentence."

Griner's detention was extended repeatedly, most recently through Dec. 20, which was the expected length of her trial. If convicted, Griner, 31, faces up to 10 years in prison and also has a right to an appeal.

The U.S. government classified Griner's case on May 3 as "wrongfully detained," meaning the U.S. will more aggressively work to negotiate her release even as the legal case against her plays out, the State Department has said.

White House press secretary Karine Jean-Pierre told reporters last week that Griner's guilty plea will have "no impact" on any of the negotiations to bring her home to the U.S.

Calls to free Griner escalated following the April release of U.S. Marine veteran Trevor Reed, who was freed from a Russian prison as part of a prisoner exchange. Former Marine Paul Whelan has also been detained in Russia since late 2018.

"We're going to do everything that we can to bring home Brittney Griner safely, and to also make sure that we bring Paul Whelan back home, as well," Jean-Pierre said.

Former New Mexico Gov. Bill Richardson is planning to travel to Russia in the near future for talks aimed at negotiating a deal to free Griner, a source with knowledge of the proposed trip told ABC News.

Richardson, who also served as the U.S. ambassador to the United Nations and energy secretary in the Clinton administration, played a role in achieving Reed's release.

ABC News' Joseph Simonetti, Tanya Stukalova, Patrick Reevell and Henderson Hewes contributed to this report.