Some two dozen additional athletes could be barred from the Summer Olympics in Rio de Janeiro, the International Olympic Committee said Friday. Officials announced that those 23 Olympians, who competed in five sports at the last Summer Games, in 2012 in London, were newly suspected of having doped.  The I.O.C. retested 265 doping samples from London using new scientific methods, it said Friday, discovering possible evidence of past drug use by athletes who could compete in Rio in 10 weeks. The I.O.C. said it could not immediately identify the implicated athletes for legal reasons and was in the process of informing the athletes and the six national Olympic committees to which they belonged.  The reanalysis of the London samples was part of continuing broad scrutiny of athletes who have competed in recent Olympics.  Earlier this month, officials announced they had retested 454 doping samples from the 2008 Summer Games in Beijing, discovering suspicious results among 31 athletes from 12 countries and six sports. On Friday, the I.O.C. said it had identified one additional suspicious sample from Beijing.  The Russian Olympic Committee revealed this week that its athletes accounted for nearly half of that Beijing group. Among them were 11 track and field athletes, two weight lifters and a rower, according to Russian state media reports.  A step-by-step look at how Russian agents used an elaborate scheme to swap out tainted urine samples for clean ones taken months earlier.  Both the Beijing and London retesting results came in the wake of a detailed account this month by the former longtime director of Russia’s antidoping lab, Grigory Rodchenkov, who said he worked for years at the direction of the Russian government to help the country’s top athletes use performance-enhancing substances and go undetected. Just before the London Games, he said, he created a cocktail of three anabolic steroids and liquor used by Russia’s top athletes with a chance at winning medals.  Dr. Rodchenkov, who has a Ph.D. in analytical chemistry, told The New York Times that Russian athletes had doped leading up to Beijing, London and throughout the course of the 2014 Sochi Games, when Russia controlled the Olympic testing laboratory. He described an overnight operation in which he switched tainted urine for clean urine, collected from athletes in the months before competition and passed surreptitiously through a hole in the wall of the lab building.  The I.O.C. has called Dr. Rodchenkov’s account “very detailed and very worrying,” deferring to the World Anti-Doping Agency to verify it. Last week, the agency announced an independent investigation into the allegations. That inquiry is expected to conclude by July 15, exactly three weeks before the Rio Games begin.  “Time is of the essence,” said Lauryn Williams, a sprinter and bobsledder from the United States who is a member of the World Anti-Doping Agency’s athletes’ committee. “We’re two short months away from the Games, and we’re in the middle of the biggest doping scandal. It just keeps coming.”  The president of the I.O.C., Thomas Bach, said on Friday that he had appointed a disciplinary commission to proceed against the dozens of athletes affected by the Beijing and London retests. Those athletes will have the right to have their additional doping samples from the Games in question — stored separately in Switzerland, for quality control — tested as well.  Seeking to reassure athletes and other various constituencies on Friday, the I.O.C. emphasized that its continuing reanalysis of past doping samples — which the organization has the ability to do for up to 10 years after competition — was initially more narrowly focused on keeping drugged athletes out of this Summer’s Games.  “We can’t have faith in the 2012 results,” said Ms. Williams, the first American woman to have won medals at both the summer and Winter Olympics. “There are people who have been cheated out of their opportunity to stand on the podium in the past. We can’t go into Rio and then try to backpedal.”
Scrutiny of London Olympians’ doping samples has put athletes from six countries under new suspicion, the I.O.C. said.