The president of Russia, Vladimir V. Putin, articulated a possible legal strategy on Wednesday for scores of Russian athletes preparing to defend themselves in sports doping prosecutions: casting doubt on the chain of custody for their urine samples.
“When we provided the test samples, there were no complaints,” Mr. Putin said, going on to describe the microscopic scratches on glass sample bottles that investigators said showed that Russia’s Federal Security Service had cracked into them to switch out the athletes’ incriminating urine.