Have they? That's the first I hear about that.
As far as I know the only time they did test old urine samples (from 1999), they did test positive, but the case was dropped because the urine was claimed to have been stored incorrectly.
That's true, but the effect you had from doping back then (until the 80's) was marginal compared to the last 20 years. EPO really is/was a wonder product for cyclists. It had an enormous effect.
Therefor, there is also no doubt in my mind he was doped. There is no way you would be so dominant in cycling's biggest doping-era without being doped yourself. There are too many other factors as well pointing to that. Most of his first lieutenants and team mates who were excellent when in Armstrong's service suddenly turned to crap after they left US Postal and/or were caught for doping in the years that followed.
And then there's also the ties to doping doctor Ferrari.
Armstrong has not been cleared for doping by the way. The US Attorny has just decided to drop the criminal law suit. But the American anti-doping agency has already said this doesn't mean they will drop their case against him.
I think this criminal case was more about the possible drug trafficking and organised distribution in the team, rather than Armstrong taking them.