A cyclist who was a U.S. Anti-Doping Agency witness against Floyd Landis in 2007 pleaded guilty on Wednesday to conspiracy to distribute human growth hormone and another performance-enhancing drug he imported from China.

Joe Papp, 34, of the Pittsburgh suburb of Bethel Park, pleaded guilty to two counts of conspiracy to sell HGH (Human Growth Hormone) and Erythropoietin, or EPO, over the Internet.

Papp earned more than $80,000 selling the drugs from September 2006 to September 2007 to 187 customers "including cyclists and other athletes, throughout the United States and internationally," Assistant U.S. Attorney Mary McKeen Houghton said.

None of the customers was identified in court, and Houghton, Papp and his attorney, William Ward, declined to comment on terms of the plea agreement, which was sealed by the court. Often that is done if a defendant is cooperating with the government, but Ward and Houghton refused to say if that was the case.

Papp's Chinese connection is identified only by the name "Chen" and authorities did not say if that person would be charged. The evidence against Papp is largely in e-mails between him and his customers, a Web site he operated through which the drugs were sold, and a private mail box where Papp allegedly received the drugs.

"The e-mails would also show that no prescriptions were written by medical doctors and that the drugs were sold for use to enhance athletic performance," Houghton told the judge.

Papp has admitted using performance enhancing drugs since testosterone metabolites were found in his urine at a Turkish cycling tour in May 2006, and was later suspended from cycling for two years.

Since then, he's perhaps best known for his links to Landis, who was stripped of his 2006 Tour de France win because of doping allegations, and another American cyclist, Kayle Leogrande, who sued the USADA in an effort to stop the anti-doping agency from completing a drug test on him.

At Wednesday's hearing, Houghton mentioned Landis' 2007 doping trial in detailing Papp's background for Chief U.S. District Judge Gary Lancaster.

At the trial, Papp acknowledged his long pattern of drug use and testified about the ways synthetic testosterone helped him recover after races. Papp didn't implicate Landis as a doper, but was questioned by USADA attorneys to counter claims by Landis' attorneys who argued that testosterone wouldn't help a cyclist win a race like the Tour de France.

Papp testified that the hormone "definitely does have a beneficial therapeutic effect" and said it was possible to elude detection in drug tests by using a gel form of the hormone at specific times after races.

Papp had testified that he started using testosterone after first using EPO, a hormone produced by the kidney that stimulates the production of red blood cells. Use to treat certain forms of anemia, the drug helps athletes by increasing the capacity of their blood to carry oxygen.

Two days ago, a French judge issued an arrest warrant for Landis so he can be questioned about alleged computer hacking at a French lab where samples collected before his 2006 Tour de France victory showed abnormally high testosterone levels. Landis called it another attempt by the lab to fabricate evidence against him.

In the Leogrande case in 2008, USADA attorneys introduced cell phone records showing more than 270 calls and texts between Papp and Leogrande, and pictures of Leogrande holding vials of EPO at Papp's home.

Leogrande also received a two-year doping ban for using the drug after suing to prevent the USADA from testing his backup urine sample after his original sample was deemed "clean" because of technicality.

Papp faces up to five years in prison on each of the conspiracy charges when he's sentenced June 25.