An explanation emerged Wednesday, when the United States Anti-Doping Agency released its dossier on Armstrong, citing witness testimony, financial records and laboratory results. Armstrong was centrally involved in a sprawling, sophisticated doping program, the agency said, yet he employed both cunning and farcical methods to beat the sport’s drug-testing system.



The report also introduced new scientific evidence that, according to the agency, suggested Armstrong was doping during the last two times he competed in the Tour de France.



“It has been a frequent refrain of Armstrong and his representatives over the years that Lance Armstrong has never had a positive drug test,” the report said. “That does not mean, however, he did not dope. Nor has Armstrong apparently had nearly as many doping tests as his representatives have claimed.”



As part of its investigation, Usada asked Christopher J. Gore, the head of physiology at the Australian Institute of Sport, to analyze test results from 38 blood samples taken from Armstrong between February 2009 and the end of last April. Those taken during the 2009 and 2010 Tours de France, the report said, show blood values in which the likelihood “of occurring naturally was less than one in a million” and other indications of blood doping.



While not a conventional antidoping test, Usada concluded that the findings “build a compelling argument consistent with blood doping.”



The techniques used by Armstrong and his teammates to elude positive tests were widely used by many cyclists, and many believe those tactics are still in use today. They often exploited weaknesses in the antidoping system, many of which still persist.



The most basic technique outlined in the report, based on affidavits from some of Armstrong’s former teammates, was simply running away or hiding.



“The most conventional way that the U.S. Postal riders beat what little out-of-competition testing there was, was to simply use their wits to avoid the testers,” the report concluded.



To facilitate out-of-competition testing, professional cyclists are required to inform their national antidoping agencies of their locations at all times. Any rider who receives three warnings in an 18-month period for either providing their whereabouts inaccurately or not filing the information at all can be punished as if they had a positive drug test.



Noting that “the adequacy of unannounced, no-notice testing taking place in the sport of cycling remains a concern,” Usada outlined several methods used by Armstrong and his teammates to circumvent the system.



The simplest was pretending not to be home when the testers arrived. As long as they were in the city they had reported as their locations, the riders found they would not receive a warning for not answering the door.



The agency compared the whereabouts information it received from Armstrong over the years with messages between Armstrong and Michele Ferrari, a sports medicine doctor who is also a target of the doping investigation. There were revealing discrepancies, the report said.



Travel plans that Armstrong conveyed months in advance to Ferrari through training and racing diaries were submitted to Usada weeks later, sometimes the day he made the trip. While those last-minute changes did not break any rules, they frustrated the agency’s testing plans. The doping agency also found that Armstrong often stayed at a remote hotel in Spain where he “was virtually certain not to be tested.”



According to the report, Armstrong abruptly dropped out of one race after his teammate George Hincapie warned him through a text message that drug testers were at the team’s hotel. Armstrong had, Hincapie said in an affidavit, just taken a solution containing olive oil and testosterone.