A German doctor accused of masterminding an international blood-doping network admitted on Tuesday to helping athletes undergo transfusions to boost performance.
Lawyers for the 42-year-old sports physician Mark Schmidt said he had started to aid individuals in 2012 but refrained from disclosing specific names.
Charges against him allege the doping of athletes at the 2014 and 2018 Winter Olympics, the 2016 Rio Sumer Games, and at cycling's Giro d'Italia and Tour de France.
Facing up to ten-years in jail, Schmidt claimed he made no financial gain from the process but asked for 5,000 euros ($5,852) a year for his services and also asked for result-based bonuses.
"Why did I decide to practice blood doping, I don't remember anymore. Doping has to be done these days if you want to succeed," he said.
"In the end I never made money from it, I always saw it as a hobby," he added.
He is accused of helping skiers and cyclists from eight countries including retired six-time Tour de France stage winner Alessandro Petacchi.
Schmidt has been in custody since he was arrested in Germany in February 2019 as part of Operation "Aderlass" -- or "blood letting" in German -- which involved raids at the Nordic world skiing championships in Austria.
Five athletes and two suspects were detained at the venue two hours before the start of the men's 15km cross-country event. One Austrian athlete was caught undergoing a blood transfusion.
As part of the wider Aderlass case, Austrian cyclist Georg Preidler was given a 12-month suspended sentence for sports fraud by a court in Innsbruck in July.
Blood doping is aimed at boosting the red blood cells, which allows the body to transport more oxygen to muscles, increasing stamina and performance.
This is the first major prosecution under anti-doping legislation introduced in Germany in 2015.
The trial is expected to finish by December 21.