Walsh is single-minded: he believes the American rider has used banned substances.
Along with French writer Pierre Ballester, Walsh has written 'LA Confidential - The secrets of Lance Armstrong', soon to be published and with the main allegations already splashed across this week's L'Express, a weekly French magazine.
Armstrong strenuously denies that he has ever taken performance enhancing drugs.
Walsh repeats the "secret" that is 1999 Armstrong failed a test for triamcinolone, a corticosteroid which is found in some medicines and creams. The UCI did not take any action against Armstrong.
More damaging claims are made in the book by Irishwoman Emma O'Reilly, a former physiotherapist with the US Postal team. She told Walsh Armstrong took the blood-boosting erythropoietin, EPO.
O'Reilly worked with the US Postal team for three and a half years from 1998. She claims she was asked by Armstrong to dispose of bags containing syringes after the end of the Tour of Holland in 1998 and that in May 1999 she was asked to drive to Spain to collect drugs and bring them back into France, which she later handed to Armstrong.
Armstrong's legal team has warned Walsh he now faces a costly legal battle.
Walsh has faced down such threats before. Since 2001 he has linked Armstrong with Italian doctor Michele Ferrari,
formerly the team doctor to the Gewiss-Ballan team, which he was forced to leave after he claimed that EPO, if used properly, was no more harmful than orange juice.
Walsh claimed that Armstrong made several consultation trips to see Ferrari in Italy. Armstrong countered by saying he was consulting with Ferrari on advanced training methods.