I can't prove he used drugs anymore than he can prove he did not use drugs.
Almost all pro bicycle races have used drugs. Are you telling me that 1 guy who never used drugs was able to beat all of the guys who used drugs x years in a row?
I think it is highly likely his cancer was caused by drugs. Cancer defintely changed his physique so that he could win a race like the Tour de France. Did you know one of the biggest side effects of the experimental cancer drug that he used was increased red blood cell count? That is aim of most of the drugs cyclists use.
Common sense he says he used drugs. At least 4 former teammates have been busted for drugs. He used Micahel Ferrari as his physician for years. Ferrari has been linked to providing many riders with EPO and educating them how to use it without getting caught. And there is much, much, more.
What I thought was most damning was the testimony from a really good friend of his and his wife at a trial.
Ex-Friends Say Armstrong Admitted Drug Use : NPR
Contrary to popular belief he has failed at least 1 drug test. He managed to produce a doctor's note after the test and they execused it. Doubt if they would do that any more.
Maybe in x years he will come clean.
He defintely is a good rider and since they pretty much are all using drugs I kind of think it makes it fair.