A bit of pop psychology here.
For the likes of Samu and Indurain, being so intimately involved with the sport than us clinicians, knowing the tests can be beaten, and the system can be cheated, to come out to actually say Armstrong was innocent because of no positive spoke volume. What they were doing was actually reflecting onto themselves, saying that, "I never tested positive, so they can't come after me." Because it's abnormal for a clean pro to be so bent out of shape on positive tests. Clean pros know the dirty ones have been getting away with it. That's why clean pros wouldn't be the least bit surprised if Armstrong had been doing all the things said in the USADA report.
Uncaught criminals tend to be sympathetic towards caught criminals because they identify with the life of trying to cheat the system all the time. So much effort to conceal the truth, so for a fellow criminal to be caught, they tend to speak against that because they don't want to be caught themselves, so they'd give reasons why certain individual should be innocent.
Unfortunately, unless Samu gets caught or someone squeals on him, he won't get in trouble because his own national federation is a joke.