Those questions percolated across the mushing community on Tuesday, leaving many perplexed. Aliy Zirkle, who finished eighth this year and has raced against Seavey for a decade, called him “an honest and upstanding Iditarod competitor,” not the type to break rules.

“I do not think that he gave those drugs to his dogs,” Zirkle said in an email. “Obviously his dogs were given drugs — but by whom or why? I don’t know.”

The thought that another musher would taint Seavey’s dogs sounded unlikely to his competitors. The sport is a tight and insular one, in constant need of sponsors and promotion, and setting off a doping scandal would hurt the sport as much as it would damage Seavey. And Tramadol would be a strange drug choice; it is not commonly used in the world of dogsledding. Royer said she had never heard of it.

That reasoning led some to speculate that outsiders who protest the Iditarod and similar events might be involved.

“There are people in the world who truly believe that dog mushing is cruel and should be banned,” Zirkle said. “Of course, this is far from the truth, but lies can be told about any subject and some people believe them. I guess the question is: Are there really people radical enough to actually give drugs to his dogs in order to undermine an honest, hardworking good man? Crazy speculation, I know! But that seems to be all we are left with now.”

Unless, of course, Seavey did it. The Iditarod Trail Committee, which stages the event, does not seem convinced. It did not discipline Seavey, nor ask him to return the $59,637 he won in prize money, because it could not prove intent, as was required by race rules. After the positive tests emerged, the first ones since the race began drug testing the dogs in 1994, the group examined rules in other sports and realized it was virtually alone in not placing the burden of proof on the athlete — in this case, the musher, not the dogs. It changed the rule earlier this month and, in announcing those changes, brought Seavey’s drug-test results to light.