HARLOW, ENGLAND - JANUARY 19:  An analyst prepares a sample for testing in the anti-doping laboratory which will test athlete?s samples from the London 2012 Games on January 19, 2012 in Harlow, England. The facility, which will be provided by GSK and operated by King?s College London, will test over 6250 samples throughout the Olympic and Paralympic Games. Over 150 anti-doping scientists will work in the laboratory, which measures the size of seven tennis courts, 24 hours a day.  (Photo by Oli Scarff/Getty Images)
British doctor accused of doping 150 athletes
A British doctor is denying allegations that he's been providing performance enhancing drugs to 150 elite athletes. CNN's Fred Pleitgen reports.
02:13 - Source: CNN
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HARLOW, ENGLAND - JANUARY 19:  An analyst prepares a sample for testing in the anti-doping laboratory which will test athlete?s samples from the London 2012 Games on January 19, 2012 in Harlow, England. The facility, which will be provided by GSK and operated by King?s College London, will test over 6250 samples throughout the Olympic and Paralympic Games. Over 150 anti-doping scientists will work in the laboratory, which measures the size of seven tennis courts, 24 hours a day.  (Photo by Oli Scarff/Getty Images)
British doctor accused of doping 150 athletes
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