Olympic gold medalist Antonio Pettigrew admitted publicly for the first time Thursday that he used performance-enhancing substances during a long, successful sprinting career in which he passed all drug tests.

The admission came during the last day of testimony for the government in the trial of his former coach, Trevor Graham, who is accused of lying to federal authorities investigating doping in sports. Graham has pleaded not guilty.

It was also revealed Thursday that Olympic sprint champion Justin Gatlin worked undercover for authorities investigating doping in sports, according to the testimony of IRS agent Erwin Rogers.

Rogers testified that Gatlin, who once shared the world record in the 100 meters, secretly recorded several telephone calls with Graham. U.S. District Judge Susan Illston barred Rogers from disclosing any more details of the calls.

Gatlin, who has served half of a four-year ban for doping, tested positive for excessive testosterone at the Kansas Relays in 2006, his second doping violation. He has maintained he never knowingly took a performance-enhancing drug.

Gatlin has asked the Court of Arbitration for Sport to cut his suspension nearly in half so he can compete at the Beijing Olympics. Gatlin, like Pettigrew, was once a member of Graham's Sprint Capitol USA team in Raleigh, N.C., which also included sprinters Marion Jones and Tim Montgomery — both of whom are now imprisoned.

Pettigrew testified that Graham encouraged him in 1997 to inject human growth hormone and the oxygen-boosting drug EPO, both banned in track. Soon after, Pettigrew said, he began buying the drugs from Angel "Memo" Heredia, an admitted steroids dealer from Laredo, Texas.

Once he began taking the banned substances, Pettigrew said he was able to run 400 meters in the 43-second range for the first time.

"I was running incredible times as I was preparing for track meets," Pettigrew said during 30 minutes of testimony. "I was able to recover faster."

Pettigrew initially lied to federal investigators and denied doping when they first talked to him in February 2005. But he finally confessed behind doors to cheating when confronted with documents in October 2006 strongly suggesting drug buys from Heredia.

Thursday was his first public admission.

Pettigrew won a gold medal as part of the 1,600-meter relay team at the 2000 Sydney Olympics. He retired from track in 2002 and is now an assistant coach at the University of North Carolina.

It is unclear what sanctions, if any, Pettigrew will face for his confession. University officials in Chapel Hill, N.C., said they are reviewing the matter.

"In our view, if Mr. Pettigrew, or any athlete who competed in the finals of the men's 4x400 meter relay during the 2000 Games, did so while using a banned substance, that would undermine the validity of the result the team achieved," U.S. Olympic Committee Chief Executive Officer Jim Scherr said in an e-mail. "If an athlete who ran in the finals knowingly and purposely engaged in cheating, the medals won by the entire team are tarnished and, in our view, should be returned."

Scherr said any decision to strip Pettigrew of his medal rests with the International Olympic Committee and the International Association of Athletics Federation.

The other members of that gold medal relay team were Michael Johnson and brothers Alvin and Calvin Harrison. Also on the team, but not running in the final, were Jerome Young and Angelo Taylor.

The IOC tried several years ago to strip Johnson and the other members of the team of their gold medals after Young tested positive for drugs and was banned for life. But the Court of Arbitration for Sport overruled the IOC and said the entire team should not be disqualified. That allowed Pettigrew to keep his medal.

The two officials with the U.S. Anti-Doping Agency attending Graham's trial, including managing director Dr. Larry Bowers, referred calls to the agency's chief executive Travis Tygart on whether Pettigrew will be investigated for cheating. Tygart and other officials at USADA headquarters in Fort Collins, Colo., didn't return telephone calls.

Three other disgraced track stars who also were coached by Graham followed Pettigrew to the stand to testify about their own drug use.

Garfield Ellenwood said Graham got steroids for him after the two discussed the sprinter's desire to break records, which never occurred. He also testified that Graham introduced him to Heredia, which is important because Graham is also charged with lying about his relationship with Heredia.

Graham told investigators that he talked to Heredia on the telephone only once in 1996. But prosecutors contend Graham and Heredia worked closely over several years to supply Graham's athletes with performance-enhancing drugs.

Ellenwood said he now is the coach of the Liberian Olympic track team and will attend the Beijing Games. He is also the head track coach at Bethune-Cookman University in Daytona Beach, Fla.

Ellenwood also testified that after he retired in 2002 he obtained prescriptions from Dr. Ramon Scruggs for a variety of steroids, EPO and human growth hormone, all of which are legal to take with a doctor's prescription.

A federal grand jury indicted Scruggs in April on steroid distribution counts, alleging he dealt drugs to major league baseball players. Scruggs has pleaded not guilty.

Young and Dennis Mitchell, both of whom won Olympic gold medals, each testified that Graham introduced them to Heredia, who then became their drug supplier.

The government called its last witness Thursday and the judge refused Graham's lawyer's request to toss out the case. Graham's lawyer, William Keane, said he is undecided about whether he'll call any witnesses. The jury could began deliberating as soon as Tuesday.