In what is now well understood and accepted by Armstrong and his accusers, in 1999 Armstrong used a prohibited steroid in a race prior to the Tour de France, which was detected in doping tests at the Tour. The USADA Reasoned Decision explains (here in PDF):
On the first day of the Tour Lance seized the yellow jersey by winning the prologue. A few days later the USPS team was notified that Armstrong had had a corticosteroid positive. According to those who were there, Armstrong did not have a medical authorization at the time to use cortisone and the positive drug test result set off a scramble. Tyler Hamilton remembers, “a great deal of swearing from Lance and Johan, and Dr. del Moral repeating, ‘¡Qué lío!’”Tyler said, the “general understanding was that they were scrambling to come up with something because Lance had used cortisone without medical authorization.”Armstrong admitted that events transpired as related by O'Reilly in his inteview with Oprah Winfrey.
Emma O’Reilly was in the room giving Armstrong a massage when Armstrong and team officials fabricated a story to cover the positive test. Armstrong and the team officials agreed to have Dr. del Moral backdate a prescription for cortisone cream for Armstrong which they would claim had been prescribed in advance of the Tour to treat a saddle sore. O’Reilly understood from Armstrong, however, that the positive had not come from a topical cream but had really come about from a cortisone injection Armstrong received around the time of the Route du Sud a few weeks earlier. After the meeting between Armstrong and the team officials concluded, Armstrong told O’Reilly, “Now, Emma, you know enough to bring me down.”
Today, following a report in a Belgian newspaper that Armstrong had actually failed four drug tests in the1999, not just the one that was admitted by UCI at the time, the UCI released its 9-page statement in an apparent effort to absolve itself of any responsibility. The new information comes from a leaked internal UCI memo which Cycling News has published.
However, the memo does exactly the opposite. It shows that Armstrong had tested positive for the steroids three times prior to the UCI press release of 21 July 1999, and once after. The UCI failed to release that information in 1999, and in fact, implied that there was only one failed test on July 4, 1999. Even more remarkably, during the events of the past year when the full scope of Armstrong's doping became widely known and accepted, UCI continued to keep secret the 1999 tests. It is very difficult to come to any conclusion other than UCI was being economical with the truth back in 1999 and has continued to do so -- leading to an obvious question: Why?
I'm not sure what has become of the idea of a full investigation of UCI, but clearly there are skeletons rattling around in its closet.
Here is that 1999 press release courtesy of UCI: