The U.S. Anti-Doping Agency is investigating whether track coach Alberto Salazar encouraged star runner Galen Rupp and others to skirt anti-doping rules, the Associated Press reported Wednesday.
A person with knowledge of the investigation told the AP that more than a dozen witnesses have been interviewed and USADA is actively pursuing documents and other evidence from Salazar, who coached Rupp to the silver medal in the 10,000 meters at the London Olympics.
The person spoke on condition of anonymity because anti-doping investigations are considered confidential.
A story by ProPublica and the BBC this month contained allegations from former Salazar assistant Steve Magness and a former Salazar runner, Kara Goucher, that Salazar skirted the rules.
On Wednesday, Salazar published a 12,000-word letter online disputing the allegations.
Salazar's open letter, released on the eve of U.S. championships, says the Oregon Project he leads "will never permit doping."
Salazar detailed Rupp's history with both thyroid disease and asthma and says he properly received exemptions for medications to treat both conditions.
In his letter, Salazar said Goucher suffers from the same thyroid disease as Rupp and introduced him to the first endocrinologist who treated him.
Salazar also implies Magness was jaded because he was fired from the Oregon Project in 2012, and that while Magness "makes a number of inflammatory and false statements about the Oregon Project and me personally, at no point does he allege that any doping violations occurred while he was with the Oregon Project. That's because none did."
It is a lengthy, detailed screed by arguably the world's most powerful long-distance running coach -- one that comes after nearly a month's worth of almost-daily doping allegations that have come out since the BBC-ProPublica story.
Salazar disputes every one of them, both in general terms -- "The Oregon Project will never permit doping and athletes must fully comply with the WADA Code and IAAF Rules" -- and in very detailed, specific ways.
Notably, Salazar said Rupp has received only two therapeutic-use exemptions for the asthma medicine prednisone and none since 2012. That runs contrary to claims in the BBC-ProPublica story that the 29-year-old took the medicine continuously since he was 15. At nationals in 2011, Rupp famously ran wearing a mask to limit his pollen intake. Salazar writes he did that because he had not yet received clearance for a TUE for prednisone.
Salazar also took exception to a sentence in the story that implied Project Oregon athletes were required to have prescriptions for asthma and thyroid medication. He said 9 percent of his athletes were diagnosed with a thyroid condition after he started coaching them. He said 14 percent have been diagnosed with exercise-induced asthma, which is below the average on some recent U.S. Olympic teams.
Nike, which founded the Oregon Project in 2001, issued a statement following Salazar's rebuttal.
"We take the allegations very seriously as Nike does not condone the use of performance enhancing drugs in any manner," it said.
"Both Alberto and Galen have made their position clear and refute the allegations made against them, as shown in Alberto's open letter.
"Furthermore we have conducted our own internal review and have found no evidence to support the allegations of doping."
BBC and ProPublica also released statements saying they stood by the documentary.
Information from The Associated Press was used in this report.