Sports doctor Mark Schmidt has confessed to the use of illegal drugs and blood doping in Germany and Austria, having been involved in scandals in cycling and winter sports such as skiing.
In an ongoing trial that started on September 16, Schmidt admitted that since 2012 he had been using doping methods and given prohibited substances to athletes.
Those athletes in question were not announced during the hearing.
The 42-year-old claimed that he "did not profit from doping" and believes there was no threat to the health of the athletes he was assisting.
"It was always important for me that their health was not harmed," the confession said.
Almost 150 charges have been brought against the doctor by the Munich prosecutor's office in Germany, according to the Westdeutsche Zeitung.
It was reported that Schmidt normally received €5,000 (£4,600/$5,900) per season as a basic amount for medical care, with more intensive measures costing more.
His expenses were also large too for his special equipment for blood preparation as well as for his travel and hotels.
Six of his devices were set up in the court, with some of them previously being seized on February 27 2019 during a raid at the World Ski Championships.
During this time, Schmidt explained their functions and switched on a device for welding blood tubes, with other machines being used for preparing blood.
One of these was able to separate blood plasma and red blood cells.
Schmidt also seemed to contradict a prosecutor's charge that he administered a dangerous drug to a mountain biker, stating that he reported to the Austrian that he had not carried out any tests with the agent himself, suggesting he was not sure of the harm of the drugs.
The Operation Aderlass doping trial stems from the seizure at the World Ski Championships, which detained two Austrian athletes on the national ski team, Max Hauke and Dominik Baldauf as well as Estonians Karel Tammjärv and Andreas Veerpalu on suspicion of violating anti-doping legislation, along with Kazakh skier Alexei Poltoranin.
Two members of a doping-related criminal group were also detained.
A total of nine people were arrested and 16 searches were conducted leading to the current trial.
"The confession opens up an insight into a way of thinking that must be stunned," said Dagmar Freitag, chairman of the Sports Committee of the Bundestag and Social Democratic Party politician.
"Doping is fraud against all clean competitors and betrayal of the ethical values of sport."
A fifth defendant in the case, known as "Dirk Q" has been in custody since 2019 and is also accused of taking blood from athletes and injecting it again, including at the Pyeongchang 2018 Winter Olympics.
Schmidt did deny that he played a part in doping scandals within former cycling teams Gerolsteiner and Milram from 2007 to 2010 who disbanded due to the uncovering of doping within the squads.
A verdict is expected before Christmas, with Austrian cross-country skier Johannes Dürr supposed to testify tomorrow.
Dürr was a whistleblower for Operation Aderlass, but was handed a lifetime ban from the sport last year for his participation in doping in the sport.