Months of claims and counterclaims come to a head in a hotel conference room in Frankfurt, Germany, Thursday, when the International Skating Union considers the deliberate sabotage of a speed skate involving an American Olympic medalist and, allegedly, his former coach.

The ISU's disciplinary commission is scheduled to hear testimony behind closed doors from Simon Cho, a Vancouver Olympic bronze medalist in short track speedskating, former American short track coach Jae Su Chun, and at least two witnesses.

Cho confessed last October to deliberately bending the skate blade of Canadian athlete Olivier Jean at an international meet in Poland in 2011. Jean's skate wouldn't track properly on the ice and he was forced to withdraw from a relay.

Cho claimed that his coach, Chun, badgered him into sabotaging Jean's skate; Chun says he was not involved.

The ISU panel will essentially decide whether the skater or the coach is telling the truth, and then it will determine punishment. Both Cho and Chun could face lifetime bans from the sport.

Last week, Cho told the ISU that he would boycott the hearing, but he has since changed his mind.

Volker Waldeck, the chairman of the disciplinary commission, declined requests by Cho, Chun, and witnesses to appear at the hearing via video.

"It is important for us to determine the credibility of a witness judging his actual testimony and his demeanor during all parts of the hearing," Waldeck wrote in a letter to an attorney for one of the witnesses.

An investigation last fall by U.S. Speedskating, the American governing body of the sport, said there was not "sufficient evidence to conclude that Coach Chun directed Simon Cho to tamper with the skate." Investigators also wrote that hearing testimony that is compelled under oath would help decipher the truth.

The ISU hearing will not include sworn testimony. But Cho and Chun are each prepared to present testimony and evidence that could help the commission determine which of them is more credible.

Cho has insisted that teammate Jeff Simon was with him when Chun allegedly ordered the tampering. Simon denies that and will be in Germany to testify, according to his attorney, Ed Williams.

"Mr. Simon did not hear Coach Chun specifically tell Simon Cho to tamper with the Canadian's skate," says Williams, who has filed abuse complaints against Chun on behalf of Simon and other skaters.

"But such an instruction would not be inconsistent with what Coach Chun told the assembled U.S. team prior to the race," Williams adds.

Simon is expected to testify that Chun told the American team to be "disruptive" and "obnoxious" towards the Canadian team, which shared a locker room with the Americans at the meet.

Chun's demeanor at the meet is also a focus of the hearing. ISU rules bar such behavior by coaches.

Chun "doesn't know what the word 'obnoxious' means," says his attorney, Russell Fericks. "It's not part of his limited English vocabulary."

But Chun faces a possibly bigger hurdle with the testimony of Canadian Jean. He told NPR in October that Chun said, "I hope you lose," in the locker room in Poland. Chun once coached Jean and the Canadian team.

Fericks insists Chun was misunderstood.

"He said, 'That's not the way to win,'" Fericks says, which was a response to Chun's belief that the Canadian team had engaged in "team skating" with a Russian team, forcing Americans out of a race.

Fericks acknowledges that Chun was upset with the Canadians and was encouraging his team "to not get pushed around."

Jean is not testifying in person. Instead, he provided a statement to the commission, according to Phil Legault, a spokesman for Speed Skating Canada. Legault declined to provide the statement to NPR.

Fericks hangs Chun's credibility, especially as it relates to the tampering incident, on Jeff Simon's testimony.

"Jeff Simon has been rock solid on this from the very beginning," Fericks says, noting Simon's insistence that he was not present when Chun allegedly ordered the tampering.

"If he has a bias," Fericks adds, "his bias would be critical of the coach."

Chun has already resigned from U.S. Speedskating, which also suspended his coaching certification through the 2014 Winter Olympics.

U.S. Speedskating initially said it would conduct disciplinary proceedings for Cho, but it is now deferring to the ISU.

The ISU's Waldeck tells NPR the disciplinary commission will not make any decisions in the case immediately. The commission will issue a written decision, he says, but he does not predict when that might happen.

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