"60 Minutes" has been investigating the widespread use of performance-enhancing drugs by Russian athletes, including some who won gold medals at the Sochi Winter Olympics.

The International Olympic Committee said Thursday it's considering retesting blood and urine samples from the now-tainted Russian lab at the 2014 Winter Games. But based upon what CBS News has learned from the lab's former director, any positive drug tests disappeared a long time ago.

Dr. Grigory Rodchenkov shared details of a systematic cover-up in Sochi during Skype conversations with Vitaly Stepanov, a former Russian anti-doping official turned key whistleblower.

Stepanov allowed "60 Minutes" to listen to 15 hours of conversations he secretly recorded with Rodchenkov.

"He had the ability to help to get the necessary results," Stepanov told CBS News -- referring to gold medals.

In the recordings, Rodchenkov named Russian gold medalists in three sports -- bobsled, skeleton and cross country skiing -- whose dirty drugs tests he helped cover up.

It was all part, he said, of an elaborate scheme to protect Russia's Olympic medal winners, with the help of his country's intelligence service, known as the FSB.

"FSB tried to control every single step of the anti-doping process in Sochi," Stepanov said Rodchenkov told him.

The FSB figured out a way to open bottles considered to be tamper-proof containing urine from drug-tainted athletes. Then they filled the bottles with clean urine collected from athletes before they started doping.

Rodchenkov said he then had two weeks after the Sochi games -- to make sure, in his words, people turned out to be clean before test samples were sent to the International Olympic Committee in Switzerland for storage.

CBS News also learned Thursday a recent review of blood tests in at least one Olympic event at Sochi has revealed evidence of test tampering involving Russian athletes.