Here is the problem with "proof" as we in the Western World see it.
The burden is always to prove guilt beyond a reasonable doubt. That is a tough one, involving eye-witness testimony that must pass the evil vendetta/jealousy/hater rule. That means the person testifying against the defendant must be free of any petty malice against said defendant and must bring forth testimony without the hint of vengeance or opportunity for personal gain.
Then, there is the testing itself, which in this case doesn't hold up to scrutiny. Either there was something wrong with the handling of the samples after the fact (hence the so-called positive results from the 1999 samples can be thrown out the window) or the so-called experts are not expert enough to definitively say one way or another whether there was blood manipulation going on. Suspicion looms, but all of it circumstantial.
This, therefore, leaves the wrongdoer with plenty of wiggle room. As it stands right now there is only suspicion fueled by personal distrust and antipathy on the part of "the haters".
We are human and are not above feelings of personal dislike. But I will tell you what is certainly NOT circumstantial. Armstrong, who had never shown any particular prowess on the pro level as either a climber in the high mountains nor as a TT'ist pre-cancer comes out of nowhere to put the record for consecutive wins in the Tour out of reach.
The mere feat itself is so ridiculous it is beyond human comprehension how anyone thinks he did it clean, given the sheer audacity of the feat itself, the cast of characters he's surrounded himself with in able to do it, and his inability to excel in the two disciplines needed to become a Tour champion (climbing and TT'ing).
We may never know the answer. The people who know seem willing to go to their graves protecting the rule of "omerta" out of blind loyalty, fear of reprisal and loss of future earnings or they themselves are such sleazeballs that integrity to them means not getting caught (Bruyneel, Carmichael, Ferarri).