Howman said yesterday that Armstrong's repeated claim that he has never tested positive for a banned substance could no longer be regarded as proof of his innocence.

``What seems to have happened in this particular scenario is that it went on for many years under the noses of those who were supposed to be detecting it and at times probably with their knowledge,'' he said. 

Howman said Armstrong had finally been caught because fellow cyclists had broken a code of omerta and confessed their parts in a ``conspiracy to defraud the sport''.

He did not specifically identify the agencies or individuals he suspected may have turned a blind eye to doping by Armstrong or his teams. But he referred to ``suggestions'' contained in the report of the United States Anti-Doping Agency that irregularities in some Armstrong tests might not have been investigated as rigorously as they should have been. 

Howman said failed doping tests were no longer the benchmark needed to identify cheats. 

He used the case of Olympic track and field athlete Marion Jones to illustrate flaws in the system.

Once considered the fastest woman in the world, Jones served prison time and gave back her five medals from the 2000 Sydney Olympics after being convicted of lying to federal investigators about using performance-enhancing drugs.

Howman said the result of USADA's investigation of Armstrong was a ``compelling'' case against the seven-time Tour de France winner. 

In an earlier statement, WADA president John Fahey welcomed USADA's ``reasoned decision'' in the Armstrong case.