From a June 2004 CN update:

Any idea how Armstrong found out about Mayo's use of this stuff? Who on his team (Euskatel-Euskadi) might have ratted him out?
Level playing field?
In light of everything we now know, what the heck was Armstrong's email really about? He found out about a doping method he wasn't using, and so urging WADA and UCI to test for it so the Spaniards he was worried about (i.e. Mayo, who took 2 minutes out of him on the Ventoux in the 2004 Dauphine) couldn't use this technique to beat him? Coincidentally, Mayo flopped in the 2004 Tour.Armstrong's warning
On the eve of the second stage of the Dauphiné Libéré in France, US Postal Service spokesman Jörg Muller confirmed that Lance Armstrong did send an e-mail to the Tour de France, UCI, and WADA warning of a specific doping method, as described in former Tour adjunct director Daniel Baal's new book, released Tuesday.
Despite insinuations by the French newspaper Le Monde that Armstrong's concern over the possible use of synthetic haemoglobin (derived from bovine blood) in the peloton was directed at his Spanish rivals in particular, Baal and the team both insist that the message was one of general interest and not an attack by the American.
"I saw the e-mail with my own eyes and there was nothing mean-spirited in Armstrong's message," Baal said, quoted in Tuesday's l'Equipe. "He said it in his usual fashion: Do what you can to look into this product..."
US Postal added that "He never accused the Spanish. We're surprised that the information would come out like that, as it can only spark a fight between the riders."
Any idea how Armstrong found out about Mayo's use of this stuff? Who on his team (Euskatel-Euskadi) might have ratted him out?
Level playing field?