Berlin - German authorities said on Tuesday they have received documents from doping expert Werner Franke which he claims show Tour de France winner Alberto Contador was involved in doping.

Franke said he has documents from last year's Operation Puerto doping investigation in Spain which show that Contador, a Spaniard who won the doping-marred Tour on Sunday, had taken HMG-Lepori as a testosterone booster and an asthma product called TGN.

"We can confirm we have received the documents, and they will be incorporated into procedures of the district attorney's office," a spokesperson for Germany's Federal Criminal Police Office said.

Contador, who rides for the Discovery Channel team, missed the 2006 Tour when his former team, Liberty, was disqualified because he and four other riders - plus the team director and doctor - were allegedly linked to Operation Puerto.

The Spanish doping investigation is one of the largest scandals in cycling history - at least 50 riders are suspected of getting sophisticated drug services, including blood doping, from a Madrid clinic.

Contador said on Saturday that his name had mistakenly turned up in the Puerto file.

"I was in the wrong team at the wrong time and somehow my name got among the documents," Contador said, adding cycling's governing body corrected the mistake.

Franke, a molecular biologist, made his reputation by researching the systematic sports doping that turned the former East Germany into an Olympic powerhouse. He has clashed with Jan Ullrich, another rider linked to Operation Puerto.

A German court imposed a gag order on Franke for publicly disclosing how much the 1997 Tour winner paid the Madrid clinic. It was believed there wasn't enough evidence establishing Ullrich, who has denied doping, as a customer.

But the case is headed back to court, because Ullrich's DNA samples since have been matched to blood bags seized at the Madrid clinic. - Sapa-AP