Some of the confusion around doping charges in cycling revolves around the fact that EPO (the most-often used PED) doesn't show up on drug screens the way cocaine or other "recreational" drugs do.
Erythropoietin (EPO) is produced naturally by the human body, and all humans therefore have it in their blood. To prove a doping charge, it has to appear in such high concentrations as to appear outside a certain range. Not just the "normal" range - but the range that is statistically possible for a highly trained endurance athlete.
Further confusing the issue is the fact that professional cyclists and their doctors have become highly skilled at masking the use of synthetic EPO. Not just chemical agents (most, but not all, of which are known to anti-doping agencies) but also through the use of medical techniques such as blood transfusions: The athlete receives a transfusion of his own "clean" blood before competition or a time when he is liable to be tested. This is why testing regimes typically allow for almost continual monitoring - and an athlete has to let doping agencies know where they will be.
None of this is to say Armstrong did, or did not, use performance-enhancing drugs. There certainly aren't any "smoking gun" samples. But there ARE people who are prepared, many years after the event, to testify that he did participate. What the motivation for these people to do so is far from clear, and it certainly is possible that they have been coerced into making false assertions in exchange for immunity from prosecution.
If this were a criminal matter, Armstrong would have the protections afforded by our Constitution. But its not. The USADA is a law unto itself. And, for whatever reason, it has decided to go after the most popular and successful cyclist in a generation. A man whose fight against cancer, and against the mountains and cobblestones of the European tour, has inspired millions of people.
A sad day for Lance Armstrong and for his millions of fans. But he certainly hasn't "lost" the Tour titles he won in my eyes. All the USADA has done has to extinguish - probably forever - my interest in the sport of professional cycling.
