There is a lot of incriminating evidence against Lance Armstrong, from IM's between two former team-mates that all but said there was an organised doping ring on their team at the time, testimonies from a former female soignuer (they are the people that give the massages, carry their bags, organise food and water bottles for the upcoming racing, and basically doing all the crappy jobs in between) on what was going on at the time, and even his team manager is nicknamed the 'The Hog' from his racing days where apparently he liked to keep all the drugs to himself.
You have to realise that it is not that hard to get stuff like EPO, steriods etc. as it can be easily ordered over the internet and it is pretty cheap when you order it from China and plus there are a lot of corrupt pharmaceutical reps to which they are more then happy to sell to athletes on the side to make some more $$$$$$$. Put it this way, if is easy and cheap enough for me to get EPO from China (not that I ever have), then it wouldn't be too hard for Usain Bolt to do so. You have to factor in that Armstrong is worth a lot of money to cycling's governing body - the UCI (basically the International Cycling Union in English), that their is a lot of talk and speculation that sport's head honcho's are more then willing sweep things under the carpet, so Armstrong doesn't test positive so they can continue raking in the dough. It's the same with athletics, tennis, golf (believe it or not), and swimming. And I have heard a lot of strong talk about football as well.