Well, let's see, what's so bad about investigating the use of dope?
Uh, in this case, they're not investigating the use of dope. They go into alaboratory,where samples are being used to help refine testing techniques -- the lab is using these samples under the explicit condition that they not be used to inculpate athletes. That also means that the burden of maintaining strict control over the samples' identity is not there: there's no independent oversight, and there's no making doubly sure all the tracking information is maintained.
A magazine that happens to belong to the company that runs the TdF, and happens to have a history of launching drug accusations against LA runs an "investigative piece" where they acquire personal data from LA and match it against some of these samples that are positive. They get the guy in charge of the TdF to lament publically how LA looked him in the face and lied to him.
They don't have the evidence to nail him, and they haven't proven anything.
I'm not a cycling fan, and I've never found LA much of a personally appealing guy myself, but I recognize a cheap smear campaign.